fix(unibtc): retry flaky Bedrock reserve API and debounce its error alerts

[spalen0]

Problem

Last 12h of monitoring.service logs, unibtc task:

Issue	Runs	Effect
Rejecting Bedrock reserve API response: ['BOB (chain 60808) missing from supplies']	19:05, 23:05, 01:05, 04:05	Telegram error, PoR coverage and feeder gap skipped
Request failed for https://affiliate-api-eosin.vercel.app/...: Read timed out. (read timeout=30)	22:05, 03:05, 06:05	Telegram "API unavailable", same checks skipped
uniBTC mint baseline missing (1h=True 24h=False)	every run	Warning noise: history is younger than the 24h window since the #362 deploy

7 of 12 runs skipped the API-dependent checks.

Root cause

I polled the API for about 20 minutes. The backend recomputes every 5 minutes (06:25:07, 06:35:08, 06:40:08 UTC, plus an extra one at 06:33:09).

• A recompute takes 20–45s, and requests hang while it runs. Our hourly run at :05 often starts during a recompute, which causes the timeouts.
• One recompute can drop a chain and the next one is complete. Observed at 06:33:09: Berachain was missing and total_supply was 4395.41. At 06:35:08 it was complete again (4546.42).

Fix

• Retry in-run (up to 3 attempts): 30s after a failed request, and 5.5 min after a rejected snapshot, because a bad snapshot is served until the next recompute. Worst-case run time is about 7 min, within the hourly budget. Validation is unchanged: a rejected snapshot is still never used.
• Debounce errors: the Telegram error is sent only when the API stays unusable for 3 consecutive runs. UNIBTC_API_FAILURE_STREAK resets on success. Skipping PoR coverage for an hour is harmless because the PoR feed updates daily.
• Request errors and parse errors now raise ApiStatsError instead of sending separate messages. The fetch uses requests directly, so a timeout no longer logs an extra ERROR line.
• Mint baseline: logged at info while snapshot history is still warming up (no snapshots yet, or the 1h baseline exists but no snapshot is 20h old yet). A real gap in an established history still warns.

Testing

• uv run pytest: 1344 passed. New tests cover retry order and delays, the streak alerting only on the 3rd run, timeout wrapping, and warm-up detection.
• ruff check, ruff format: clean.
• Live load_api_stats against the real API with an isolated cache: usable, 0.3s.

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