fix: Improve error handling if walk browser profile dir

[moonD4rk]

• Implement error handling for path permission errors in chromiumWalkFunc
• Refactor firefoxWalkFunc to handle permission errors and log warnings
• Add import statement for log/slog in firefox/firefox.go

Proposed changes

If access to the browser configuration file is not permitted, print an error log and skip.

Close #345

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit, build tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)