Handle the loop closing between ThreadsafeProxy's is_closed() check and dispatch

[zigpy-review-bot]

Closes #740. Follow-up to #727 and #739 — this closes out the last members of the RuntimeError: Event loop is closed teardown-race family.

ThreadsafeProxy.func_wrapper snapshots the loop object at construction, so #739's ordering fix (publish self.loop = None before closing) can't reach it: the worker thread can close the loop between the proxy's loop.is_closed() check and the dispatch via asyncio.run_coroutine_threadsafe() / loop.call_soon_threadsafe(), and both raise RuntimeError: Event loop is closed at the caller. This wraps both dispatches in try/except RuntimeError and treats close-during-dispatch exactly like already-closed: log the existing "Attempted to use a closed event loop" warning and drop the call. The except is narrow — both try blocks wrap only the scheduling call (for the async path, call() merely constructs the coroutine; its body never runs there), so no RuntimeError from user code can be swallowed.

Two findings from pre-open review (details below) are folded in:

• Disconnected async proxy calls are now awaitable. The pre-existing is_closed() branch returned bare None for coroutine methods too, so real callers that await through a proxy (await self._gw.reset(), await self._gw.disconnect(), await self._gw.send_data(...)) got TypeError: object NoneType can't be used in 'await' expression when disconnected — trading one teardown exception for another. Both disconnected paths (already-closed and closed-mid-dispatch) now return an already-completed future for coroutine methods, so await proxy.method() resolves cleanly to None; sync calls still return None as before. On the race path the never-to-be-scheduled coroutine is explicitly closed, so it doesn't warn as never-awaited.
• EventLoopThread.run_coroutine_threadsafe() raises legibly when the loop is gone. After Clear EventLoopThread.loop before closing it #739 the shutdown-window failure there was AttributeError: 'NoneType' object has no attribute 'call_soon_threadsafe'; it now snapshots self.loop and raises RuntimeError("Event loop is not running"). The sole caller (uart.connect) already handles this via except Exception.

Two follow-up commits, from post-open review of the same family:

• The passed coroutine is closed on both of run_coroutine_threadsafe()'s failure paths. The None guard closes it before raising, and when the worker closes the loop after the snapshot (so asyncio.run_coroutine_threadsafe() itself raises RuntimeError), it is now closed before re-raising too — mirroring the proxy's async dispatch path — so neither failure mode leaks a "coroutine ... was never awaited" RuntimeWarning at teardown.
• inspect.iscoroutinefunction() replaces the deprecated asyncio.iscoroutinefunction() (deprecated since Python 3.14, removal slated for 3.16; these were bellows' only two call sites). Drop-in for every case here: real coroutine functions, plain callables, functools.partial, AsyncMock.

Tests

Five new tests. test_proxy_loop_closed_during_async_dispatch and test_proxy_loop_closed_during_sync_dispatch pin the race window by making loop.call_soon_threadsafe raise RuntimeError while is_closed() still returns False — a faithful stand-in, since a genuinely closed loop would trip the earlier guard. test_proxy_loop_closed_async pins the awaitable disconnected result on the already-closed branch; test_thread_run_coroutine_threadsafe_loop_not_running pins the RuntimeError on the None path; test_thread_run_coroutine_threadsafe_loop_closed_mid_dispatch pins the coroutine being closed (CORO_CLOSED) on the post-snapshot race path. All five fail on dev and pass with the change.

Verification

• pytest tests/ → 446 passed (Python 3.14.5), clean under -W error::RuntimeWarning -W error::DeprecationWarning (pins both the no-leaked-coroutine behavior and the deprecation removal)
• With bellows/thread.py reverted to dev: the five new tests fail (leaked RuntimeError ×2, TypeError on await None, AttributeError, leaked never-awaited coroutine), rest pass
• Pre-open review: an Opus subagent review (confirmed the except RuntimeError breadth is safe and flagged the coroutine leak on the raise path) and a Copilot CLI second opinion (GPT-5.6 Sol; flagged the await None TypeError) — both findings addressed as described
• pre-commit: autoflake, black, flake8, isort, codespell, ruff pass; pyupgrade/mypy fail on untouched files in the local hook env only (same Python 3.14 breakage as noted on Clear EventLoopThread.loop before closing it #739) — CI is the real check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.55%. Comparing base (553ec35) to head (6905629).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #741   +/-   ##
=======================================
  Coverage   99.55%   99.55%           
=======================================
  Files          64       64           
  Lines        4263     4286   +23     
=======================================
+ Hits         4244     4267   +23     
  Misses         19       19           

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