v0.5.0

• Enhanced SQLite concurrency and prevented database locks by introducing a
  database_busy_timeout parameter (defaulting to 5000ms) in
  Documentrix::Documents#initialize.
• Improved GVL-friendly waiting during lock contention via
  @database.busy_handler_timeout configuration in SQLiteCache.
• Prevented immediate SQLITE_BUSY errors on writes by updating
  SQLiteCache#[]= to use BEGIN IMMEDIATE transactions, avoiding transaction
  upgrade failures.