resource_warnings: route unclosed-resource warnings through Salt logger

[dwoz]

Summary

Python filters ResourceWarning by default, so a bare warnings.warn(..., ResourceWarning) from a __del__ finalizer is silently dropped in production. Callers that missed a close() / destroy() / context-manager contract therefore never see the intended migration signal, and the leaked resource accumulates invisibly.

Concrete incident that motivated this

After commit 0c3f53d9172 removed the __del__-based cleanup from SaltEvent / MasterMinion / RunnerClient / WheelClient in favor of a ResourceWarning-emitting __del__, out-of-tree consumers like SSEAPE that relied on GC-time cleanup via the inline pattern

salt.utils.event.get_master_event(opts, sock_dir).fire_event(...)

began leaking one unix socket per fire-and-forget instance on 3008.2+. In a VMSP master pod the leak accumulated ~350 sockets/min → +180 MB of kernel slab per hour → OOM every ~78 min at the 1 GiB pod cap. The intended ResourceWarning never reached operator logs because ResourceWarning is silenced by default in production Python and Salt didn't route it through logging.

What this PR does

• New helper salt.utils.resource_warnings.warn_until_close(message, source, category=ResourceWarning, log=None):
  • Emits the ResourceWarning (behavior preserved for dev / test / -W default::ResourceWarning).
  • Also logs the same message at WARNING level via the caller's module logger, so the signal survives Python's default filter and shows up in normal Salt logs.
  • Called only from finalizers — must never raise. Both the warnings.warn and the logger call are wrapped so interpreter-shutdown races don't propagate.
• Wired into all 8 existing finalizers:
  • salt/utils/event.py (SaltEvent)
  • salt/utils/asynchronous.py (SyncWrapper)
  • salt/transport/tcp.py (Subscriber, TCPPuller, PubServer, _TCPPubServerPublisher)
  • salt/transport/ws.py (PublishClient x2)
• Removes now-unused import warnings from the 4 files above.
• Latent bug fix: four of the eight warnings.warn sites (both ws.py sites plus two tcp.py sites) had a missing f prefix, so {self!r} was printed as the literal string instead of interpolating. Fixed as part of the migration.

Test plan

• New unit tests in tests/pytests/unit/utils/test_resource_warnings.py cover:
  • helper emits ResourceWarning AND a WARNING log record
  • falls back to module logger when no log passed
  • tolerates warnings.warn raising (interpreter-shutdown safety)
  • tolerates a broken logger
  • accepts a custom category (e.g. DeprecationWarning)
• Standalone verification of behavior (both signals fire, both broken-side cases don't propagate).
• CI green.