Release session in close() even if rollback fails

[vgvoleg]

Fixes #42

close() called rollback() first and released the session only afterwards. If rollback() raised — the expected outcome when the session was invalidated mid-request — the release was skipped, the session was abandoned and its pool slot was lost permanently.

Session release, _tx_context reset and owned pool/driver shutdown now happen in a finally, in both Connection and AsyncConnection. The rollback error is still propagated.

Test: begin(), force tx_context.rollback to raise BadSession, assert close() raises but still releases the session back to the pool.

[Copilot]

🟡 Changes recommended

The new regression test monkeypatches internal methods without restoring them, which can cause cascading fixture-teardown failures and make test failures flaky/harder to diagnose.

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Pull request overview

This PR fixes a resource-leak scenario in the YDB DB-API connection teardown path: if rollback() raises (e.g., due to an invalidated session), close() now still releases the checked-out session back to the pool and performs owned pool/driver shutdown, for both sync and async connections.

Changes:

• Update Connection.close() and AsyncConnection.close() to perform session release, _tx_context reset, and owned pool/driver shutdown in a finally block even when rollback() raises.
• Add a regression test that forces tx_context.rollback() to raise BadSession and asserts that close() still releases the session and clears connection state (sync + async variants).

File summaries

File	Description
ydb_dbapi/connections.py	Ensures close() always performs cleanup (release/reset/stop) via try/finally in both sync and async connections.
tests/test_connections.py	Adds a regression test covering the “rollback raises but close still releases session” scenario for both sync and async connections.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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