[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/compat/__init__.py

@@ -70,3 +70,13 @@ if compat_os_name in ('nt', 'ce'):
         return userhome + path[i:]
 else:
     compat_expanduser = os.path.expanduser
+
+
+def urllib_req_to_req(urllib_request):
+    """Convert urllib Request to a networking Request"""
+    from ..networking import Request
+    from ..utils.networking import HTTPHeaderDict
+    return Request(
+        urllib_request.get_full_url(), data=urllib_request.data, method=urllib_request.get_method(),
+        headers=HTTPHeaderDict(urllib_request.headers, urllib_request.unredirected_hdrs),
+        extensions={'timeout': urllib_request.timeout} if hasattr(urllib_request, 'timeout') else None)