L1 liveness probe

[frisitano]

Overview

This PR introduces an L1 liveness probe that emits an error if the timestamp of the latest header stored in the L1 watcher exceeds a threshold.

Config params

• liveness_threshold: How old (in seconds) should the timestamp of the latest header be before we trigger an error log.
• liveness_check_interval: How frequently (in seconds) should we check for liveness.

[codspeed-hq]

Merging this PR will not alter performance

✅ 2 untouched benchmarks

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_{Comparing feat/l1-liveness-probe (10e6471) with main (b88371e)}