Implement HTTP 103 Early Hints as modern replacement for HTTP/2 Server Push.
This allows servers to send resource hints before the final response,
enabling browsers to preload assets in parallel.
WSGI support:
- Add wsgi.early_hints callback to environ dict
- Apps can call environ['wsgi.early_hints'](headers) to send 103 responses
- Silently ignored for HTTP/1.0 clients (don't support 1xx responses)
ASGI support:
- Handle http.response.informational message type
- Apps can await send({"type": "http.response.informational", "status": 103, ...})
HTTP/2 support:
- Add send_informational() method to HTTP2ServerConnection
- Add async send_informational() method to AsyncHTTP2Connection
- Wire up early hints in gthread worker for HTTP/2 requests
Includes unit tests and Docker integration tests for all protocols.
75b46bf6cf