Implement automatic cleanup of stale cache entries

[shaypal5]

Summary

• Addresses issue TypeError: cannot pickle '_thread.lock' object #26
• add cleanup_stale and cleanup_interval parameters
• implement stale-entry deletion in each backend
• periodically run cleanup in cachier decorator
• document new feature and defaults
• add tests for pickle backend cleanup

Testing

• ruff check .
• mypy --install-types --non-interactive src/cachier
• pytest tests/test_cleanup.py -q -m pickle

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https://chatgpt.com/codex/tasks/task_e_68761d7d53e48323ba091be1ae2af698

[Borda]

wondering if all the # type: ignore[arg-type] are required instead of addressing it... Could you share the trace?

[shaypal5]

wondering if all the # type: ignore[arg-type] are required instead of addressing it... Could you share the trace?

Me too. It's the first time I used Codex. Maybe it's a pet peeve of this model specifically. I think it's running mypy for type check; it might be coming from there.