feat: support `anyio`, sending denial response, handshake headers

[WSH032]

Summary

Added

• support asyncio and Trio through AnyIO
• support sending websocket denial response
• support sending headers during websocket handshake
• add tests for hypercorn server

Changed

• remove path parameter in proxy method
• the return signature of ReverseWebSocketProxy.proxy has been changed; it no longer returns StarletteResponse, but instead returns True

Test

• fix the warnings in the tests by not using deprecated APIs from httpx

Checklist

• [x] I've read CONTRIBUTING.md.
• [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.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.41667% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 96.39%. Comparing base (977d9c1) to head (3d2b0ea).

Files	Patch %	Lines
src/fastapi_proxy_lib/core/websocket.py	84.09%	10 Missing and 4 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #34 +/- ## ========================================== - Coverage 96.74% 96.39% -0.35% ========================================== Files 9 9 Lines 461 472 +11 Branches 67 73 +6 ========================================== + Hits 446 455 +9 - Misses 9 11 +2 Partials 6 6 ```

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[WSH032]

The test succeeded on Windows but failed on Linux, preventing us from merging. Unfortunately, I don't have time to address this issue at the moment. If someone is willing to pick it up, I can provide guidance.

Need Improvement

• Revert: feat!: remove path parameter in proxy method The downstream is already passing this parameter. Let's issue a deprecation warning in this version and remove it in the next version.
• Revert: the return signature of ReverseWebSocketProxy.proxy has been changed in this commit Let's keep the original signature so users can handle responses themselves; we should provide a helper method to assist users in sending denial responses rather than sending responses ourselves.

TODO

• Use ... to represent default parameters instead of importing these private variables from httpx-ws

  https://github.com/WSH032/fastapi-proxy-lib/blob/3d2b0ea27a0b083886c1d03e37645bb5a7050dfa/src/fastapi_proxy_lib/core/websocket.py#L39-L44

• Fix: can not receive the websocket close reason

  https://github.com/WSH032/fastapi-proxy-lib/blob/3d2b0ea27a0b083886c1d03e37645bb5a7050dfa/tests/test_ws.py#L212-L215 This is an upstream issue of ASGI, and we are unable to address it. We will track it here frankie567/httpx-ws#70.

• Fix: unable to read the content of WebSocketUpgradeError.response

  https://github.com/WSH032/fastapi-proxy-lib/blob/3d2b0ea27a0b083886c1d03e37645bb5a7050dfa/src/fastapi_proxy_lib/core/websocket.py#L440-L442 This is an upstream issue of httpx-ws, We will track it here frankie567/httpx-ws#69

• Use StreamingResponse in favor of Response

  https://github.com/WSH032/fastapi-proxy-lib/blob/3d2b0ea27a0b083886c1d03e37645bb5a7050dfa/src/fastapi_proxy_lib/core/websocket.py#L431-L438 This is an upstream issue of starlette, We will track it here encode/starlette#2566

[WSH032]

I am aware of such downstream use cases, so we cannot deprecate the path parameter, which can allow us to add a dynamic path prefix.