Detach DuckLake on client disconnect to prevent RDS connection leaks

[EDsCODE]

Summary

• Explicitly detaches DuckLake catalog before closing DuckDB connection
• Prevents RDS metadata connection leaks when clients disconnect

Problem

When duckgres clients disconnect, the DuckLake extension wasn't releasing its connection to the RDS PostgreSQL metadata store. This caused connection leaks:

SELECT usename, application_name, state, count(*) 
FROM pg_stat_activity 
GROUP BY 1,2,3;

     usename     |    application_name    | state  | count
-----------------+------------------------+--------+-------
 ducklingexample |                        | idle   |   170  -- leaked connections!

Eventually RDS runs out of connection slots:

FATAL: remaining connection slots are reserved for roles with privileges of the "rds_reserved" role

Solution

Run DETACH ducklake before db.Close() when a client disconnects. This ensures the DuckLake extension properly closes its RDS connection.

Test plan

• Build succeeds
• All tests pass
• Deploy and verify RDS connection count stays stable

🤖 Generated with Claude Code