ASGI extensions support

[gi0baro]

This issue tracks all the ASGI protocol extensions and the relevant state in Granian support. Dedicated issues to single extensions track the single implementation state.

ASGI extensions

• Lifespan state #94 (https://github.com/django/asgiref/blob/main/specs/lifespan.rst#lifespan-state)
• Websocket denial response (https://github.com/django/asgiref/blob/main/docs/extensions.rst#websocket-denial-response)
• HTTP/2 server push (https://github.com/django/asgiref/blob/main/docs/extensions.rst#http2-server-push) – not supported by Hyper (https://github.com/hyperium/hyper/issues/1586)
• Zero Copy Send (https://asgi.readthedocs.io/en/latest/extensions.html#zero-copy-send) – not applicable to Granian as involving unsharable file descriptors between Python and Rust
• Early Hints (https://github.com/django/asgiref/blob/main/docs/extensions.rst#early-hints)
• Trailers (https://github.com/django/asgiref/blob/main/docs/extensions.rst#http-trailers)
• File path #82