Optimize SQLite for concurrent writes in sync-client

[adamski]

SQLite can encounter "database is locked" errors under heavy concurrent write load. It's unclear if the current connection and write strategy in sync-client is optimized for this. This could become a scalability bottleneck.

To fix:

• Review the sync-client's database connection pool and transaction handling.
• Investigate SQLite's WAL (Write-Ahead Logging) mode and other optimizations for concurrent access.
• Implement changes to ensure the database can handle the expected load without errors.

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Migrated from Linear: REP-15