mypy: Add type hints

[Daverball]

Closes: #474

My curiosity got the better of me. So this is the stubs I contributed to typeshed automatically merged into the source using merge_pyi.

Afterwards I cleaned up any mistakes and completed the type hints for the internal API. I added a couple of type tests, but we could definitely add more.

I tried to keep changes to the actual code to a bare minimum. I did however change a couple of minor things. Like remove an unnecessary check for Python 2.7

You can do with these what you want, the diff is fairly large, so it will take some time to review.

[jvanasco]

I think found a typo in your stubs-

You define a Protocol here: https://github.com/python/typeshed/blob/main/stubs/WebOb/webob/cookies.pyi#L29-L31

class _Serializer(Protocol):
    def loads(self, appstruct: Any, /) -> bytes: ...
    def dumps(self, bstruct: bytes, /) -> Any: ...

I think that should read:

class _Serializer(Protocol):
    def dumps(self, appstruct: Any, /) -> bytes: ...
    def loads(self, bstruct: bytes, /) -> Any: ...

It's basically just swapping the function names.

Notice how the input/output are reversed of the other functions: https://github.com/python/typeshed/blob/main/stubs/WebOb/webob/cookies.pyi#L96-L104

class JSONSerializer:
    def dumps(self, appstruct: Any) -> bytes: ...
    def loads(self, bstruct: bytes | str) -> Any: ...

class Base64Serializer:
    serializer: _Serializer
    def __init__(self, serializer: _Serializer | None = None) -> None: ...
    def dumps(self, appstruct: Any) -> bytes: ...
    def loads(self, bstruct: bytes) -> Any: ...

Note that SignedSerializer uses JSONSerializer if no serializer is supplied:

https://github.com/Pylons/webob/blob/main/src/webob/cookies.py#L705-L706

And CookieProfile uses the Base64Serializer

https://github.com/Pylons/webob/blob/main/src/webob/cookies.py#L813-L814

[Daverball]

@jvanasco Good catch. Feel free to open an issue or PR on typeshed.