fix: fix staticcheck issues in the verifier pkg

[qba73]

This PR:

• addresses issues highlighted by staticcheck (ref: Staticcheck reports using deprecated functions/methods and structs #531)
• fixes in this PR are limited to the package verifier

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 8 lines in your changes missing coverage. Please review.

Project coverage is 80.92%. Comparing base (02cc632) to head (3708324).

Files with missing lines	Patch %	Lines
verifier/verifier.go	42.85%	8 Missing ⚠️

❌ Your patch check has failed because the patch coverage (42.85%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #537   +/-   ##
=======================================
  Coverage   80.92%   80.92%           
=======================================
  Files          36       36           
  Lines        3355     3355           
=======================================
  Hits         2715     2715           
  Misses        493      493           
  Partials      147      147           

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[Two-Hearts]

LGTM

[Two-Hearts]

@qba73 Looks like the test coverage is below the patch target. Please see the Codecov report for details: #537 (comment)