perf(tests): significantly improve test execution time

[staticxterm]

This PR refactors the test infrastructure to significantly improve the test execution speed.

🚀 Performance

Test runtime improved substantially:

Locally (on my machine)

• Before: ~7 minutes (430s)
• After: ~1.5 minute (95s)
• ~4.5x faster

Key changes

• Switched core fixtures (settings, cli, db) to session scope to reuse MongoDB connections.
• Run init_beanie() once per test session instead of per test.
• Added an automatic database cleanup fixture to ensure test isolation and to reset the model cache because of the new "shared" approach.
• Added time-machine test dependency for deterministic cache-expiration testing instead of introducing real delays.
• Minor test cleanups and lint configuration adjustments.

Result

• Faster test execution
• Reduced database/client initialization overhead
• Deterministic cache behavior in tests
• More consistent and maintainable test setup

[CAPITAINMARVEL]

looks good nice speed up

[Riverfount]

LGTM