test: add unit tests for RandStringBytesMask and GetRunID in stringutils

[Prakhar-Shankar]

What this PR does / why we need it:

Adds unit tests for RandStringBytesMask and GetRunID functions in pkg/utils/stringutils/string.go.
The tests are table-driven and include edge case validation (e.g., n = 0).
This improves the overall test coverage of utility packages.

Which issue this PR fixes:
Fixes #752

Special notes for your reviewer:

• Achieves 100% coverage for string.go file.
• Tests verified locally with:

  go test -cover ./pkg/utils/stringutils
  
  

Checklist:

• Fixes Add unit tests for pkg/utils folder #752
• PR messages has document related information
• Labelled this PR & related issue with breaking-changes tag
• PR messages has breaking changes related information
• Labelled this PR & related issue with requires-upgrade tag
• PR messages has upgrade related information
• Commit has unit tests
• Commit has integration tests
• E2E run Required for the changes

[Prakhar-Shankar]

Hey @uditgaurav, @ksatchit , @ispeakc0de, can you please review the unit test please, thanks <3