Bridge teardown's skip-archive path now also waits for pending uploads and reports timeouts
When a remote bridge session tears down and skips archiving, it now waits on a pending-uploads check if there are uploads still in flight, and logs a new failure reason, skip_archive_flush_timeout, if that wait doesn't finish in time. The teardown telemetry now also includes the fields hold_preflush_ms and hold_preflush_landed on this skip-archive path, which previously only recorded them on the full-archive path.
This brings the skip-archive teardown path in line with the full-archive path, so timing and success information about the pre-teardown upload flush is captured consistently regardless of which teardown path runs.
Whether this behavior is active for any given account depends on the tengu_bridge_repl_teardown gate, which is unread for this account, so…