[codex] Isolate Parakeet prerecorded test imports

[tianmind-studio]

Summary

• Add lightweight cachetools.TTLCache, utils.other.endpoints.timeit, and Prometheus metric stubs inside test_parakeet_prerecorded.py.
• Keep the Parakeet prerecorded batch STT tests runnable in a lightweight Windows backend unit venv without importing Firebase auth, cachetools, or Prometheus just to collect the test.
• Preserve the real backend package paths and existing Parakeet/Scipy/WebSocket stubs already used by this file.

Root cause

test_parakeet_prerecorded.py already stubs most of the heavy STT dependencies, but importing utils.stt.pre_recorded still imports utils.byok and utils.other.endpoints. In a lightweight Windows unit-test environment without the full backend requirements installed, collection failed before any Parakeet assertions ran:

• python -m pytest backend\tests\unit\test_parakeet_prerecorded.py --collect-only -q --tb=short -> ModuleNotFoundError: No module named 'cachetools'

After fixing collection, the streaming factory subtests also imported utils.async_tasks, so the test needs a tiny Prometheus stub unless the full requirements or the shared Prometheus test fallback are already present.

Validation

• python -m pytest backend\tests\unit\test_parakeet_prerecorded.py --collect-only -q --tb=short -> 31 tests collected
• python -m pytest backend\tests\unit\test_parakeet_prerecorded.py -q --tb=short -> 31 passed
• python -m pytest backend\tests\unit\test_action_item_date_validation.py backend\tests\unit\test_parakeet_prerecorded.py -q --tb=short -> 57 passed
• python -m black --check --line-length 120 --skip-string-normalization backend\tests\unit\test_parakeet_prerecorded.py
• python -m py_compile backend\tests\unit\test_parakeet_prerecorded.py
• git diff --check
• scripts/pre-commit