Add faster Normal implementation

[aloctavodia]

Distributions in PreliZ are wrappers around SciPy distributions. This is fine for many situations, but when iterative operations are required like in optimization we could benefit from faster implementations.

This could also be used to avoid duplication of code and efforts, for instance in Kulprit we also need fast logpdf evaluations.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.39779% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 86.25%. Comparing base (f0a63bc) to head (9fc1336).

Files	Patch %	Lines
preliz/distributions/normal.py	85.36%	12 Missing ⚠️
preliz/distributions/distributions.py	86.04%	6 Missing ⚠️
preliz/internal/distribution_helper.py	77.77%	2 Missing ⚠️
preliz/tests/test_dist_scipy.py	97.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #344      +/-   ##
==========================================
- Coverage   86.70%   86.25%   -0.45%     
==========================================
  Files          38       40       +2     
  Lines        4303     4425     +122     
==========================================
+ Hits         3731     3817      +86     
- Misses        572      608      +36     

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