* fix(relay): destroy a pooled client whose session the server ended, and mark work that never ran
pg keeps calling a client queryable until its socket's end arrives, so a client released after
57P01 (pg_terminate_backend, shutdown) or a dropped socket went back to the pool and failed the
next caller's statement with 'Connection terminated unexpectedly'. Such clients are now released
with the error, so pg-pool discards them.
Also marks failures where no statement of the operation reached the server (acquire, a failed
BEGIN, a client dead at checkout) so a caller can tell work safe to re-run.
* fix(relay): skip ROLLBACK on an ended session, drop unused nothing-ran marking
Adds 57P04/57P05 to the session-ended codes and covers 08xxx, a dropped
socket, an ordinary 23505, and a real pg_terminate_backend.
Claude-Session: f2fe8cb5
