Add linters that check for bugs

[lucacome]

Proposed changes

Adds linters that check for bugs and fixes errors.
See first commit for the errors.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING guide
• I have proven my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have ensured the README is up to date
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch on my own fork

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 3.86%. Comparing base (4fca542) to head (1e062c0).

Files	Patch %	Lines
collector/nginx_plus.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #779      +/-   ##
========================================
- Coverage   3.86%   3.86%   -0.01%     
========================================
  Files          5       5              
  Lines       1319    1321       +2     
========================================
  Hits          51      51              
- Misses      1268    1270       +2     

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