Finalize connection initialization transactions

[auden-rovellequartz]

Problem

ConnectionPool.set_connection() runs new-connection hooks and an optional
liveness query, commonly SELECT 1;, but does not finalize the transaction
those operations can start when DB-API autocommit is disabled.

This is observable with PostgreSQL when a long-lived process initializes DAL at
module-import or worker-startup time, outside a request lifecycle. Because no
request teardown follows, pg_stat_activity can show that connection as
idle in transaction indefinitely, with SELECT 1; as its last query.

The behavior was diagnosed in a persistent OVXS deployment by Auden
RovelleQuartz of Omnia Value Exchange Systems.

Change

After the connection hooks and optional active-connection check complete
successfully, set_connection() now commits the resulting initialization
transaction when either the hooks ran or the active check was performed.

This gives connection acquisition an explicit transaction boundary for:

• newly opened connections; and
• pooled connections checked before reuse.

Why commit

A rollback could undo SQL-based session configuration performed by
after_connection hooks. Committing, rather than rolling back, preserves
successful initialization while ending the implicit transaction.

This occurs before the connection is returned to application code, so no
caller-owned transaction exists at this boundary.

If both connection hooks and active checking are disabled, set_connection()
does not add a commit.

Tests

The regression tests model transaction state and cover:

• fresh connections;
• pooled connection checkouts; and
• connection hooks when active checking is disabled.

Validation performed against upstream commit
6fd518e09ac4fcf64408abb2259222251c870356:

• Focused regression suite: 3 tests passed
• Complete suite on Linux: 400 tests passed, 11 skipped
• Complete suite on Windows with Python 3.13: 400 tests passed, 12 skipped
• Ruff code check: passed
• Ruff format check: passed
• Python compilation: passed
• Git whitespace validation: passed

Reproduction outline

1. Configure a PostgreSQL DAL connection with DB-API autocommit disabled.
2. Initialize DAL in a persistent process without entering a normal web-request lifecycle.
3. Do not issue an application query or invoke DAL request cleanup.
4. Inspect the connection from another PostgreSQL session using pg_stat_activity.

Before this change, the initialized backend can remain idle in transaction,
with the connection-test query as its last statement. After this change, the
backend is idle with no open transaction.