all: fix test lint issues detecte by tenv and thelper linters

[peczenyj]

here I try to handle two kinds of issues with tests

1. the usage of os.Setenv in tests that need specific env vars and we need to revert the changes in the end. This usually is done via defer + some cleanup function BUT it may not run in many cases (like in a t.Fatal) and t.Setenv already do this and it is battle tested. for this I used the linter tenv via gitlabci-lint.
2. the miss of t.Helper() in many test helpers. This was done by using the linter thelper via gitlabci-lint. The motivation is here: https://github.com/kulti/thelper?tab=readme-ov-file#why

this should have no impact in existing code or tests, but may help identify an issue from unit tests or benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.40%. Comparing base (e0e5901) to head (0657092).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3441      +/-   ##
==========================================
- Coverage   73.41%   73.40%   -0.02%     
==========================================
  Files         113      113              
  Lines       14947    14947              
==========================================
- Hits        10974    10972       -2     
- Misses       3199     3201       +2     
  Partials      774      774              

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[vangent]

Thanks!