Implement core/consensus/metrics

[varex83]

Most likely it's better to implement this on-demand

[emlautarom1-agent]

Port audit — core/consensus/metrics

• Status: 🟡 in review — PR feat(consensus): implement metrics for consensus #470
• Charon source: core/consensus/metrics — 68 non-test Go LOC (142 total)
• Complexity: Simple — Prometheus metric definitions/helpers for consensus instrumentation
• Internal deps: app/promauto (no Pluto equivalent yet — metrics currently live in crates/tracing/metrics.rs)
• Critical path: ⏸ No — instrumentation only

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Automated progress audit (2026-06-15). New comment only — no existing issue content was modified.