Continuous round monitor for time-based decryption

[ylembachar]

Adds tests/continuous, a black-box monitor that runs the full time-based round against a deployed API on a loop: get_data_for_encryption, encrypt locally, register_identity, wait for the decryption timestamp, get_decryption_key, decrypt. A round passes only if the plaintext round-trips, so a key that is present but
wrong fails rather than passes. Needed because tests/integration builds the router in process and so cannot say anything about a deployment.

Done

• Bounded (TEST_DURATION=26h) or unbounded (0) from the same code
• Failed rounds recorded, run continues; ALLOWED_FAILURES sets the verdict
• One log line per round with full identity, tx hash and decryption timestamp
• Summary with pass/fail counts and p50/p95/max release latency
• Behind the live build tag, so go test ./... never starts it
• Self-contained docker: own compose file, multi-stage build
• /metrics endpoint for a vmagent to scrape, matching the keyper deployments
• Polls only after the timestamp: ~2 reads per round instead of ~12
• Deployed on its own droplet, shutter-api-monitor-1003, separate region from 1003

Findings

• Release latency is 4.3s or 6.4s and nothing else: Gnosis block time. So >7s would be a real signal, not jitter.

Follow-ups

• Metrics off (METRICS_PORT=0); needs vmagent.yaml, REMOTE_WRITE_URL, alert rule
• No restart policy by design, so a standing monitor won't survive a reboot
• Raised rate limits are still a manual host edit; a clean redeploy reverts to 500/day and would break a multi-day run. Separate issue.