Add unit tests for osism/utils semaphore, redlock and task locks

[berendt]

Implements #2230.

Adds tests/unit/utils/test_init_locks.py, the third companion to
test_init_connections.py and test_init_task_output.py, covering the
concurrency primitives and global task-lock helpers in
osism/utils/__init__.py. No production code is changed — this is a
pure test addition. 40 test functions (41 cases) following the
established mocker / loguru_logs conventions of the existing suite.

Change set (commit order)

1. Add RedisSemaphore unit tests — __init__ attribute storage and
   the unconditional semaphore: key prefix (including the
   already-prefixed input → double prefix); acquire() first-try
   success, full-window timeout returning False, per-iteration
   zremrangebyscore cleanup, the default-10s and explicit-timeout
   fallbacks, and a fresh uuid.uuid4() per call; release()
   idempotency; and the __enter__/__exit__ context-manager protocol
   (returns self, raises TimeoutError containing the key, always
   releases, never swallows exceptions). time.time/time.sleep/
   uuid.uuid4 are patched so the acquisition loop is deterministic.
2. Add create_redlock and create_netbox_semaphore unit tests —
   create_redlock returns the pottery.Redlock built with
   key/masters={redis}/auto_release_time (default 3600 and a
   custom value), forces the "pottery" logger to CRITICAL, and
   suppresses construction-time stdout/stderr (asserted via capsys).
   create_netbox_semaphore falls back to
   settings.NETBOX_MAX_CONNECTIONS or takes an explicit value, builds
   a per-URL md5-derived key with timeout=30 and the shared redis
   client, and produces a stable key per URL.
3. Add task-lock helper unit tests — set_task_lock,
   remove_task_lock, is_task_locked and check_task_lock_and_exit,
   including the operator-user/reason fallbacks, the JSON payload shape
   (regex-matched ISO timestamp), the .decode("utf-8") path, and the
   error-logging branches. builtins.exit and is_task_locked are
   patched for check_task_lock_and_exit.

Notes for the reviewer

• pottery.Redlock is patched on the pottery module (not imported
  into osism.utils) because production imports it lazily inside
  create_redlock — matching the issue's mocking hint.
• logging.getLogger is patched in the create_redlock tests so they
  never mutate the process-global pottery logger level (test
  isolation), addressing the issue's note about that mutable state.
• freezegun is not a dev dependency, so the set_task_lock timestamp
  is matched with a regex (^\d{4}-\d{2}-\d{2}T...) rather than frozen,
  as the issue allows.

Local verification

Per repository practice the test suite, flake8, mypy and
python-black run only in the pipenv venv / Zuul CI (the dev tools and
pottery are not installed in the base interpreter), so they were not
run locally. python -m py_compile passes. The Zuul
python-osism-unit-tests job will run the suite. The tests exercise
every branch of the targeted helpers, satisfying the ≥90 % coverage
criterion for them.

Closes #2230

Assisted-by: Claude:claude-opus-4-8

[sourcery-ai]

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