*: add metric with sync message cohorts

[KaloyanTanev]

Add a metric to showcase the different "cohorts" of sync message partial sigs. This will help us triage the nodes that usually drift from the majority. Note that this metric is assuming the majority are submitting the correct head, as it's checking each peer's submission against the majority.

Also improved the log for sync messages.

Those changes are visible in the mock "Grafana panel".

category: feature
ticket: none

[Copilot]

Pull request overview

Adds observability for sync committee sync-message “head disagreement” by grouping peers into cohorts (by head block root) and exposing cohort rank as a Prometheus metric, plus improved logging around inconsistent sync messages to aid triage.

Changes:

• Adds core_tracker_parsig_cohort_rank_total metric to count per-peer cohort-rank occurrences for sync messages.
• Introduces cohort computation and reporting logic for sync-message duties, with a dedicated warning log when multiple head roots are observed.
• Adds unit tests and a benchmark for cohort computation and cohort metric emission.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
docs/metrics.md	Documents the new cohort-rank metric.
core/tracker/tracker.go	Implements cohort computation + sync-message specific reporting/logging.
core/tracker/tracker_internal_test.go	Adds tests/benchmark for cohort computation and reporting.
core/tracker/metrics.go	Registers the new Prometheus counter vec for cohort rank.

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[codecov]

Codecov Report

❌ Patch coverage is 86.27451% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.49%. Comparing base (80ddd49) to head (bece19c).

Files with missing lines	Patch %	Lines
core/tracker/tracker.go	85.71%	4 Missing and 4 partials ⚠️
app/health/checker.go	86.95%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4587      +/-   ##
==========================================
+ Coverage   57.40%   57.49%   +0.08%     
==========================================
  Files         245      245              
  Lines       33560    33653      +93     
==========================================
+ Hits        19265    19348      +83     
- Misses      11856    11859       +3     
- Partials     2439     2446       +7     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud