weaviate-client 4.20.5+ imports `packaging` without declaring it as a dependency

## Summary

Since v4.20.5, `weaviate-client` imports `from packaging import version` at module load (in `weaviate/exceptions.py`) but `packaging` is not declared in the project's install requirements. In environments that don't already have `packaging` installed transitively, every `import weaviate` raises `ModuleNotFoundError: No module named 'packaging'`.

This is most visible in slim/minimal Python container images (e.g. `python:3.12-slim`, `python:3.14-slim`), where `packaging` is not preinstalled.

## Reproduction

```Dockerfile
FROM python:3.12.8-slim
RUN pip install --no-cache-dir weaviate-client==4.21.0
RUN python -c "import weaviate"
```

Result:
```
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/local/lib/python3.12/site-packages/weaviate/__init__.py", line 13, in <module>
    from . import (
  File "/usr/local/lib/python3.12/site-packages/weaviate/backup/__init__.py", line 3, in <module>
    from .async_ import _BackupAsync
  File "/usr/local/lib/python3.12/site-packages/weaviate/backup/async_.py", line 1, in <module>
    from weaviate.backup.executor import _BackupExecutor
  File "/usr/local/lib/python3.12/site-packages/weaviate/backup/executor.py", line 20, in <module>
    from weaviate.connect import executor
  File "/usr/local/lib/python3.12/site-packages/weaviate/connect/__init__.py", line 3, in <module>
    from .base import ConnectionParams, ProtocolParams
  File "/usr/local/lib/python3.12/site-packages/weaviate/connect/base.py", line 13, in <module>
    from weaviate.util import is_weaviate_domain
  File "/usr/local/lib/python3.12/site-packages/weaviate/util.py", line 19, in <module>
    from weaviate.exceptions import (
  File "/usr/local/lib/python3.12/site-packages/weaviate/exceptions.py", line 9, in <module>
    from packaging import version
ModuleNotFoundError: No module named 'packaging'
```

Reproducible on `weaviate-client==4.20.5`, `4.20.6`, ..., `4.21.0`. Not reproducible on `weaviate-client==4.20.4` and earlier.

## Suspected cause

In v4.20.5, [PR #1999](https://github.com/weaviate/weaviate-python-client/pull/1999) dropped the unmaintained `deprecation` dependency in favor of stdlib (`fix(deps): remove unmaintained deprecation package, use stdlib instead`).

The `deprecation` package depends on `packaging`. When it was removed from `weaviate-client`'s declared deps, `packaging` was no longer reaching the install environment transitively — but `weaviate/exceptions.py` still imports `packaging.version` directly.

## Expected behavior

`packaging` should be declared as a direct dependency of `weaviate-client` (in `pyproject.toml` / `setup.py`), so any environment that installs `weaviate-client` gets `packaging` automatically.

## Why this slips through CI

Most CI environments already have `packaging` installed because pip itself depends on it, or because an unrelated package in the test env pulls it in transitively. The bug only surfaces in minimal Python images where `import weaviate` is the first thing that needs `packaging`.

## Workaround

Add `packaging` explicitly to your own requirements file:

```text
weaviate-client==4.21.0
packaging>=23.0
```

## Suggested fix

Add to `pyproject.toml`:

```toml
[project]
dependencies = [
  ...
  "packaging>=21.0",  # used in weaviate.exceptions
]
```

Happy to send a PR if that helps.

[]