Add a small utility to create directories

[noemifrisina]

Also, closes #309

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 8 lines in your changes missing coverage. Please review.

Project coverage is 40.62%. Comparing base (0e3eecb) to head (33070db).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
src/nexgen/utils.py	27.27%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #336      +/-   ##
==========================================
- Coverage   40.65%   40.62%   -0.04%     
==========================================
  Files          49       49              
  Lines        4287     4298      +11     
  Branches      592      592              
==========================================
+ Hits         1743     1746       +3     
- Misses       2432     2440       +8     
  Partials      112      112              

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