TRUNCATE checkpoint every 50 writes causes B-tree corruption on large
databases (65K+ pages) due to the exclusive-lock I/O pressure from
checkpointing thousands of frames at once.
Switch periodic _try_wal_checkpoint() to PASSIVE mode which does not
require an exclusive lock and cannot corrupt pages under I/O pressure.
Keep TRUNCATE in close() and pre-VACUUM paths where it is safe
(infrequent, controlled conditions).
Also replace silent `except Exception: pass` with logged warnings for
checkpoint failures so operators can detect early corruption signals.
Fixes#45383
