[networking] Rewrite architecture (#2861)

New networking interface consists of a `RequestDirector` that directs
each `Request` to appropriate `RequestHandler` and returns the
`Response` or raises `RequestError`. The handlers define adapters to
transform its internal Request/Response/Errors to our interfaces.

User-facing changes:
- Fix issues with per request proxies on redirects for urllib
- Support for `ALL_PROXY` environment variable for proxy setting
- Support for `socks5h` proxy
   - Closes https://github.com/yt-dlp/yt-dlp/issues/6325, https://github.com/ytdl-org/youtube-dl/issues/22618, https://github.com/ytdl-org/youtube-dl/pull/28093
- Raise error when using `https` proxy instead of silently converting it to `http`

Authored by: coletdjnz

yt_dlp/networking/__init__.py

@@ -0,0 +1,13 @@
+# flake8: noqa: 401
+from .common import (
+    HEADRequest,
+    PUTRequest,
+    Request,
+    RequestDirector,
+    RequestHandler,
+    Response,
+)
+
+# isort: split
+# TODO: all request handlers should be safely imported
+from . import _urllib