chore: optimistic block metrics

[Longarithm]

Add metrics to observe how well OB processing matches chunk production.

https://grafana.nearone.org/goto/2qb5JfcNR?orgId=1

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.24%. Comparing base (e3eeb7c) to head (4891903).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12962      +/-   ##
==========================================
- Coverage   70.25%   70.24%   -0.01%     
==========================================
  Files         855      855              
  Lines      176217   176245      +28     
  Branches   176217   176245      +28     
==========================================
+ Hits       123802   123811       +9     
- Misses      47270    47287      +17     
- Partials     5145     5147       +2     

Flag	Coverage Δ
backward-compatibility	0.35% <0.00%> (-0.01%)	⬇️
db-migration	0.35% <0.00%> (-0.01%)	⬇️
genesis-check	1.41% <0.00%> (-0.01%)	⬇️
linux	69.86% <60.00%> (-0.03%)	⬇️
linux-nightly	69.90% <100.00%> (-0.01%)	⬇️
pytests	1.72% <0.00%> (-0.01%)	⬇️
sanity-checks	1.53% <0.00%> (-0.01%)	⬇️
unittests	70.08% <100.00%> (-0.01%)	⬇️
upgradability	0.35% <0.00%> (-0.01%)	⬇️

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