BaseFilePathHandler has different working logic in Python 3.7 and Python 3.8, causing error reading files.

Seems like the difference between `typing` and `typing_extensions` is causing a problem later on in Python 3.7 vs. Python 3.8. https://github.com/p1c2u/jsonschema-spec/blob/da5e04c7b3481e62555d9c3820496030b188d1de/jsonschema_spec/handlers/protocols.py#L5-L10



Here's a quick code snippet to test, for some reason the fh object in Python 3.8 is an instance of SupportsRead, and Python 3.7 it is not.



```

from urllib.request import urlopen

from jsonschema_spec.handlers.protocols import SupportsRead



with urlopen('file:///testing.yml') as fh:         # ref#1

	if isinstance(fh, SupportsRead):               # ref#2

		print("supports read!")

		

# simplifies to the following for testing, above is just more readable

with urlopen('file:///testing.yml') as fh: isinstance(fh, SupportsRead)

```



This causes code in `file.py` to continue to `parsed_url = urlparse(uri)`. Which will give the following error: `AttributeError: '_io.BufferedReader' object has no attribute 'decode'`. This in turn causes `openapi-spec` to break when running `Spec.from_file_path` in Python 3.7 when it works in Python 3.8.



I need to go eat, but you might understand what's happening more. And I imagine you'll want it fixed as it breaks < Python 3.7 versions. I'll figure out why the diff occurs later.





## references



ref#1: https://github.com/p1c2u/jsonschema-spec/blob/da5e04c7b3481e62555d9c3820496030b188d1de/jsonschema_spec/handlers/urllib.py#L17-L18

ref#2: https://github.com/p1c2u/jsonschema-spec/blob/da5e04c7b3481e62555d9c3820496030b188d1de/jsonschema_spec/handlers/file.py#L38-L39

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