fix: revise onPrevalidationResult metrics

[twoeths]

Motivation

• Found duplicate metrics after merging feat: unbundle fixed-label metrics #460
• There are validation at gossipsub side, and validation at application side that cause the duplicate metric names

Description

• Name the validation in gossipsub "preValidationResult" to distinguish to the validation result coming from application
• Also fix meshPeerChurnEventsUnknown metric

[codecov-commenter]

Codecov Report

Patch coverage: 4.25% and project coverage change: -0.94% ⚠️

Comparison is base (23bf0ee) 82.30% compared to head (9bce1ff) 81.37%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #464      +/-   ##
==========================================
- Coverage   82.30%   81.37%   -0.94%     
==========================================
  Files          48       48              
  Lines       12039    12173     +134     
  Branches     1286     1285       -1     
==========================================
- Hits         9909     9906       -3     
- Misses       2130     2267     +137     

Files Changed	Coverage Δ
src/metrics.ts	16.43% <3.74%> (-2.57%)	⬇️
src/index.ts	69.87% <100.00%> (-0.11%)	⬇️

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