* Set default query timeout to 2 minutes and enforce minimum.
* Add statement_timeout for PostgreSQL DSN.
* Implement busy timeout for SQLite with a minimum of 2 minutes.
* Enforce minimum connection timeouts of 10 minutes for server instance.
* Introduced NewConnectionFromDB function to create connections from existing *sql.DB instances.
* Added ExistingDBProvider to wrap existing database connections for dbmanager features.
* Implemented tests for NewConnectionFromDB and ExistingDBProvider functionalities.