fix: pathsend handling in middlewares

[gi0baro]

Summary

Closes #2613

It seems that when I introduced support for pathsend in #2435 I didn't check the included middlewares to also support the relevant ASGI messages. Affected Starlette versions 0.36.0 and onwards when running on a server supporting pathsend.

Note: this is still in draft since I'd like to plan some tests for the involved code; also the proposed solution isn't necessarily the best one, probably someone like @Kludex might review this and give his feedbacks before proceeding further. Update: I added tests just to verify the code. In case you're unhappy with the implementation, we can refactor that and keep the tests.

Checklist

• [X] I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• [X] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [ ] I've updated the documentation accordingly.

[gi0baro]

@Kludex any updates on this?

[gi0baro]

Closing this in favour of #2649, as discussed.