Add mol-backoff-test formula for integration testing exponential backoff
with short intervals (2s base, 10s max) to observe multiple cycles quickly.
Fix await-signal to use --since 1s when subscribing to activity feed.
Without this, historical events would immediately wake the signal,
preventing proper timeout and backoff behavior.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
3f724336f4