[whoekage]

Fixes #1261

A reserved connection released while the pool is ending was returned to the pool via onopen(c), so Connection.end() kept waiting for it and sql.end() never resolved. release() now terminates the connection when ending is set, and returns it to the pool otherwise as before.

Adds a test that reserves a connection, calls sql.end(), releases the connection afterwards and awaits end().

Verified with the full npm test (esm, cjs, deno) on Node 24 / PostgreSQL 17 in a container replicating the CI workflow (PostgreSQL from pgdg with tests/pg_hba.conf, ssl, wal_level = logical, a second PostgreSQL on 5433):

• with this change: 3/3 runs clean, 795 passed
• master with only the new test: the new test times out and the process does not exit
• pristine master: 2 of 3 runs crash with an unrelated CONNECTION_ENDED unhandled rejection, so that one is pre-existing