Add chunked transfer encoding support to the ASGI worker for HTTP/1.1
streaming responses that don't have a Content-Length header. This fixes
SSE (Server-Sent Events) connections not closing properly.
Without chunked encoding or Content-Length, HTTP/1.1 clients wait for
the connection to close to determine end-of-response, causing streaming
endpoints to hang.
Also updates the celery_alternative example to use FastAPI with the
native ASGI worker and uvloop, demonstrating async task execution with
proper SSE streaming.
ce352dc230