Add job for ticket garbage collection and implement stale ticket handling

[tuhalf]

This pull request introduces a ticket expiration and garbage collection system for P2P objects, primarily focusing on cleaning up stale ticket objects from the database. It modifies the storage and retrieval logic for objects, adds new periodic cleanup jobs, and includes supporting tests to ensure stale tickets are properly expired and removed.

I am not sure about if I delete tickets that's used for payments or not. I need you to check that @dominicletz

[gemini-code-assist]

Summary of Changes

Hello @tuhalf, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request establishes a robust system for managing the lifecycle of P2P ticket objects within the database. By introducing automatic garbage collection and defining clear criteria for ticket staleness, it ensures that the system remains efficient and free of outdated data, improving overall database health and performance. The changes encompass schema modifications, new background jobs, and integrated staleness checks during object retrieval.

Highlights

• Automated Ticket Garbage Collection: Introduced a new hourly cron job named 'Ticket GC' that automatically prunes stale P2P ticket objects from the database, preventing the accumulation of expired data.
• Staleness Criteria for Tickets: Implemented logic to determine if a ticket is 'stale' based on two criteria: a time-to-live (TTL) of 24 hours since storage, and an epoch-based check to ensure tickets are not significantly older than the current blockchain epoch.
• Database Schema and Object Handling Updates: Modified the p2p_objects table to include a stored_at timestamp. Object storage (put_object) now records this timestamp, and object retrieval functions (object, scan, objects) now automatically filter out and delete stale objects upon access.
• Comprehensive Testing: Added new unit tests to verify the correct behavior of stale ticket expiration based on TTL and the functionality of the garbage collection process.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable ticket expiration and garbage collection system for P2P objects, which will help maintain the database by cleaning up stale ticket objects. The implementation includes a database migration for a stored_at timestamp, a new cron job for periodic cleanup, and logic to filter stale objects on read. My review focuses on potential performance improvements and enhancing code clarity. I've identified that the prune_stale_objects function could lead to high memory usage with a large database and have suggested a more scalable batching approach. Additionally, I've provided suggestions to make some parts of the code more idiomatic and concise. Regarding your question about deleting tickets used for payments, the current logic correctly implements a cleanup strategy for a distributed cache. It assumes that tickets that are old (by time or epoch) are no longer relevant, which is a reasonable approach as submitted tickets are recorded on-chain.