fix: Prometheus metrics prefix

[m3diumrare]

Most default Prometheus or Prometheus-like systems reject metrics names that don't match [a-zA-Z_:][a-zA-Z0-9_:]*

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.26%. Comparing base (df8c2bb) to head (f7650e4).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3231   +/-   ##
=======================================
  Coverage   59.26%   59.26%           
=======================================
  Files        2066     2066           
  Lines      169624   169624           
=======================================
  Hits       100521   100521           
  Misses      60311    60311           
  Partials     8792     8792           

Flag	Coverage Δ
sei-chain-pr	62.36% <100.00%> (?)
sei-db	70.41% <ø> (ø)

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Files with missing lines	Coverage Δ
utils/metrics/metrics_util.go	70.47% <100.00%> (ø)

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