Add neg_log_pdf private method

[aloctavodia]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.84615% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 82.78%. Comparing base (456d582) to head (2dd1663).

Files	Patch %	Lines
preliz/distributions/bernoulli.py	62.50%	3 Missing ⚠️
preliz/distributions/binomial.py	75.00%	2 Missing ⚠️
preliz/distributions/beta.py	80.00%	1 Missing ⚠️
preliz/distributions/halfnormal.py	80.00%	1 Missing ⚠️
preliz/distributions/negativebinomial.py	80.00%	1 Missing ⚠️
preliz/distributions/normal.py	85.71%	1 Missing ⚠️
preliz/distributions/poisson.py	80.00%	1 Missing ⚠️
preliz/distributions/weibull.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #354   +/-   ##
=======================================
  Coverage   82.78%   82.78%           
=======================================
  Files          50       50           
  Lines        5006     5048   +42     
=======================================
+ Hits         4144     4179   +35     
- Misses        862      869    +7     

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