Adopt Turso-inspired performance patterns for Xavier database

[iberi22]

This change implements several performance optimizations inspired by Turso:

1. Batch Inserts: Added insert_*_batch methods to CodebaseDb to speed up repository indexing.
2. Lazy Schema: Database tables are now created only upon the first access, reducing overhead for inactive projects.
3. LRU Cache: ConnectionManager now uses moka to maintain a fixed-size pool of active connections with an idle timeout.
4. Async Migration: Fully migrated the codebase database layer to libsql with an asynchronous API, improving concurrency and resource utilization.
5. Worker Offloading: Heavy operations like FTS population are now handled asynchronously.

Fixes #427

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PR created automatically by Jules for task 8136287466530014244 started by @iberi22

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