fix(utils/filename): handle files beginning with a period or without ext

[cjpearson]

(#184)

This change resolves the issue reported with files containing no extension. It also adds tests for filenames such as .gitignore or .env which begin with a period.

[pi0]

❤️

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.30%. Comparing base (bdab761) to head (8cf6c12).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
- Coverage   99.45%   99.30%   -0.15%     
==========================================
  Files           4        4              
  Lines         364      289      -75     
  Branches      114      119       +5     
==========================================
- Hits          362      287      -75     
  Misses          2        2              

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