[siddham-jain]

@csmarchbanks

Fixes #535.

Decorating an async def function with Histogram.time(), Summary.time(), Gauge.time(), Counter.count_exceptions() or Gauge.track_inprogress() currently wraps only the creation of the coroutine, not its execution. So the decorators silently record wrong data, e.g. a FastAPI endpoint that awaits for 100ms is observed as ~1µs, raised exceptions are not counted, and the in-progress gauge is back to 0 before the body runs. The wrapper is also no longer a coroutine function, so inspect.iscoroutinefunction() returns False for it.

Changes:

• Backport coroutine support from upstream decorator 4.1 into the bundled decorator.py: FunctionMaker.create generates an async def wrapper with return await when the caller is a coroutine function (and make uses DEF.search so that template parses). Signatures stay preserved as before.
• context_managers.py uses an async caller for coroutine functions, so the with block spans the awaited call. Sync functions take the same path as before.
• Tests for all five decorators on async def functions, including overlapping calls via asyncio.gather, plus a note in the instrumenting docs.

This picks up the direction discussed in #535 now that Python 2 is gone, and supersedes the stalled #767, whose tests cover the same cases.

[squat]

yay, this is a great start for implementing Async support here

[chrikrah]

@siddham-jain async tests fail on base, signatures survive. Mergeable after a rebase.

# git archive 40b8532, Python 3.12.3, prometheus_client imported from the export
$ python -m pytest tests -q -p no:cacheprovider --ignore=tests/test_asgi.py --ignore=tests/test_twisted.py --ignore=tests/test_aiohttp.py
421 passed, 2 skipped, 28 subtests passed
$ python -m pytest tests/test_core.py -q -p no:cacheprovider   # both files from base ff9a2d3
5 failed, 120 passed   # the five *async* decorator tests
$ python -I probe.py   # @h.time() on: async def f(a, b=2, *, c)
(a, b=2, *, c) True f   # inspect.signature, iscoroutinefunction, __name__
$ git merge-tree --write-tree --name-only origin/master 40b8532   # master e2f2bf9
CONFLICT (content): Merge conflict in tests/test_core.py
# not run: Python 3.9 to 3.11, the three ignored suites, the suite on a merge with master

non-blocking: keep import math (#1225) and import inspect.

Async series jump from ~1µs to real latency. Worth an upgrade note?