Add faster HalfNormal distribution

[aloctavodia]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.74699% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 84.07%. Comparing base (fd9fcb6) to head (f4ae608).

Files	Patch %	Lines
preliz/distributions/halfnormal.py	86.07%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
+ Coverage   84.05%   84.07%   +0.01%     
==========================================
  Files          42       43       +1     
  Lines        4567     4610      +43     
==========================================
+ Hits         3839     3876      +37     
- Misses        728      734       +6     

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