test(pgsql): regression test for poisoned-transaction recovery with JSON event logging (#6084)

Context

#6084 reported an ASAN heap-use-after-free: recovering a poisoned PostgreSQL transaction logged CurrentQuery after the frontend packet had already been freed. Commit 0959fa9cf fixed it by calling RequestEnd() before l_free(pkt->ptr) in PgSQL_Session::handler_poisoned_simple_query().

The regression test requested in #6084 was never added. pgsql-tx_poisoned_recovery-t covers backend termination followed by ROLLBACK, but it does not enable the events log. The freed pointer is read only on the event-logging path (PgSQL_Logger::log_request() → PgSQL_Event::write_query_format_2_json()), so the current test would not detect a reintroduction of the bug.

Scope

• Extend pgsql-tx_poisoned_recovery-t or add a new test that sets pgsql-eventslog_filename and pgsql-eventslog_format to JSON (format 2) before triggering poisoned-transaction recovery.
• Cover ROLLBACK, and ideally COMMIT, after a backend is terminated mid-transaction (SQLSTATE 57P01).
• Assert that the recovery statement is present in the JSON events log with the expected query text.
• Restore the logging variables on exit.
• Register the test in the appropriate group in test/tap/groups/groups.json. The test is most useful when it also runs in the ASAN CI fan-out.

Acceptance

• The test passes on current v3.0.
• Under ASAN, the test fails if the order of RequestEnd() and l_free() in handler_poisoned_simple_query() is reverted.