fix: avoid cross-loop session reuse in Weixin direct sends

[LeonSGP43]

Summary

• only reuse the live Weixin adapter when its send session belongs to the current event loop
• fall back to a fresh one-shot aiohttp session for cross-loop media sends
• add regression coverage for same-loop reuse and cross-loop fallback

Testing

• python3 -m pytest -o addopts='' tests/gateway/test_weixin.py

Closes #13305.

[alt-glitch]

Competing fix with #13350, #13520, #12810 — all address same cross-loop Weixin session reuse bug. Maintainers should pick one.

[alt-glitch]

Competing fix with #13350, #13520, #12810.

[teknium1]

Thanks for the focused regression fix. The member discussion correctly identified this as one of several competing fixes; current main already implements the requested behavior.

Automated hermes-sweeper review evidence:

• a22465e07ab4b71019f711e7a6463f6590c50742 (fix(weixin): send_weixin_direct cross-loop session check) fixes the same aiohttp cross-loop TimerContext failure described here.
• gateway/platforms/weixin.py:2307-2336 reuses the live adapter only when send_session._loop is asyncio.get_running_loop(); a different-loop session falls through to a new aiohttp.ClientSession for text and media delivery.
• The fix shipped in v2026.5.7.

Closing as already implemented on current main.