Fails to build on free-threaded Python 3.14

Currently, `pip install zopfli` fails on the free-threaded build with the following error:

```
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/command/bdist_wheel.py", line 285, in _validate_py_limited_api
          raise ValueError(
          ...<4 lines>...
          )
      ValueError: `py_limited_api='cp310'` not supported. `Py_LIMITED_API` is currently incompatible with `Py_GIL_DISABLED`. See https://github.com/python/cpython/issues/111506.
```

Python 3.15 will add a new `abi3t` stable ABI that is supported on the free-threaded build. I'm actively working on adding support for abi3t in setuptools (https://github.com/pypa/setuptools/issues/5205) so hopefully you'll be able to use that for Python 3.15 and newer.

For now though I think just adding some logic in `setup.py` to disable limited API builds on the free-threaded build will help a lot, since build errors are hard to work around. As a followup, adding official free-threaded support and uploading free-threaded wheels would also be great.

See [the free-threaded Python guide](https://py-free-threading.github.io) for more details about supporting the free-threaded build. I'm one of the primary authors and am happy to answer more questions.

Full install log:

<details>

```
goldbaum at Nathans-MacBook-Pro in ~/Documents/py-zopfli on fix-free-threaded-builds!
(.venv) ± pip install zopfli
Collecting zopfli
  Using cached zopfli-0.4.1.tar.gz (179 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Installing backend dependencies ... done
  Preparing metadata (pyproject.toml) ... error
  error: subprocess-exited-with-error

  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> [81 lines of output]
      /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/dist.py:287: UserWarning: Unknown distribution option: 'test_suite'
        warnings.warn(msg)
      toml section missing PosixPath('pyproject.toml') does not contain any of the tool sections: ['setuptools_scm', 'vcs-versioning']
      toml section missing PosixPath('pyproject.toml') does not contain any of the tool sections: ['setuptools_scm', 'vcs-versioning']
      /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/dist.py:765: SetuptoolsDeprecationWarning: License classifiers are deprecated.
      !!

              ********************************************************************************
              Please consider removing the following classifiers in favor of a SPDX license expression:

              License :: OSI Approved :: Apache Software License

              See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
              ********************************************************************************

      !!
        self._finalize_license_expression()
      running dist_info
      creating /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info
      writing /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/PKG-INFO
      writing dependency_links to /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/dependency_links.txt
      writing requirements to /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/requires.txt
      writing top-level names to /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/top_level.txt
      writing manifest file '/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/SOURCES.txt'
      /private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/normal/lib/python3.14t/site-packages/vcs_versioning/overrides.py:609: UserWarning: No GlobalOverrides context is active. Auto-creating one with SETUPTOOLS_SCM prefix for backwards compatibility. Consider using 'with GlobalOverrides.from_env("YOUR_TOOL"):' explicitly.
        return get_active_overrides().subprocess_timeout
      listing git files failed - pretending there aren't any
      reading manifest file '/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/SOURCES.txt'
      reading manifest template 'MANIFEST.in'
      adding license file 'COPYING'
      writing manifest file '/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli.egg-info/SOURCES.txt'
      creating '/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-modern-metadata-rekagfgr/zopfli-0.4.1.dist-info'
      Traceback (most recent call last):
        File "/Users/goldbaum/Downloads/.venv/lib/python3.14t/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 389, in <module>
          main()
          ~~~~^^
        File "/Users/goldbaum/Downloads/.venv/lib/python3.14t/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 373, in main
          json_out["return_val"] = hook(**hook_input["kwargs"])
                                   ~~~~^^^^^^^^^^^^^^^^^^^^^^^^
        File "/Users/goldbaum/Downloads/.venv/lib/python3.14t/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py", line 175, in prepare_metadata_for_build_wheel
          return hook(metadata_directory, config_settings)
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/build_meta.py", line 380, in prepare_metadata_for_build_wheel
          self.run_setup()
          ~~~~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/build_meta.py", line 317, in run_setup
          exec(code, locals())
          ~~~~^^^^^^^^^^^^^^^^
        File "<string>", line 86, in <module>
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/__init__.py", line 117, in setup
          return distutils.core.setup(**attrs)  # type: ignore[return-value]
                 ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/core.py", line 186, in setup
          return run_commands(dist)
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/core.py", line 202, in run_commands
          dist.run_commands()
          ~~~~~~~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/dist.py", line 1000, in run_commands
          self.run_command(cmd)
          ~~~~~~~~~~~~~~~~^^^^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/dist.py", line 1107, in run_command
          super().run_command(command)
          ~~~~~~~~~~~~~~~~~~~^^^^^^^^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/dist.py", line 1019, in run_command
          cmd_obj.run()
          ~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/command/dist_info.py", line 99, in run
          bdist_wheel = self.get_finalized_command('bdist_wheel')
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/cmd.py", line 318, in get_finalized_command
          cmd_obj.ensure_finalized()
          ~~~~~~~~~~~~~~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/_distutils/cmd.py", line 119, in ensure_finalized
          self.finalize_options()
          ~~~~~~~~~~~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/command/bdist_wheel.py", line 250, in finalize_options
          self._validate_py_limited_api()
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
        File "/private/var/folders/1k/qnk13d854239ztdf9n4_f7n00000gn/T/pip-build-env-0pcm7yyo/overlay/lib/python3.14t/site-packages/setuptools/command/bdist_wheel.py", line 285, in _validate_py_limited_api
          raise ValueError(
          ...<4 lines>...
          )
      ValueError: `py_limited_api='cp310'` not supported. `Py_LIMITED_API` is currently incompatible with `Py_GIL_DISABLED`. See https://github.com/python/cpython/issues/111506.
      [end of output]
```

</details>

[]