Honor HTTP methods in make_asgi_app like make_wsgi_app

[00200200]

make_wsgi_app already rejects non-GET requests (405) and answers OPTIONS with Allow. make_asgi_app ignored scope["method"] and always scraped.

That means a POST/PUT/HEAD to the ASGI metrics app currently returns 200 plus a full exposition, and OPTIONS never advertises the allowed methods.

@csmarchbanks this matches the existing WSGI behavior rather than inventing a new contract.

Reproduction

from prometheus_client import CollectorRegistry, make_asgi_app, make_wsgi_app

registry = CollectorRegistry()
wsgi = make_wsgi_app(registry)

def start_response(status, headers, exc_info=None):
    print("WSGI", status)

list(wsgi({"REQUEST_METHOD": "POST", "PATH_INFO": "/metrics", "QUERY_STRING": ""}, start_response))
# WSGI 405 Method Not Allowed

ASGI before this change returns 200 for the same POST.

Tests

tests/test_asgi.py:

• OPTIONS → 200, Allow: OPTIONS,GET, no scrape
• POST → 405, Allow: OPTIONS,GET, no scrape
• /favicon.ico → empty 200, no scrape (same as WSGI)

python -m pytest tests/test_asgi.py tests/test_wsgi.py tests/test_exposition.py tests/test_core.py — 224 passed, 1 skipped.