Refactor priors

[dweindl]

Introduces Distribution classes for handling prior distributions, sampling from them, and evaluating negative log-priors (#312). Later on, this can be extended to noise models for measurements and computing loglikelihoods.
This also adds a notebook demonstrating the various prior options which are a common source confusion, and fixes a faulty test.

Closes #311.

👀 notebook: https://petab--329.org.readthedocs.build/projects/libpetab-python/en/329/example/distributions.html

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.57746% with 29 lines in your changes missing coverage. Please review.

Project coverage is 74.90%. Comparing base (9a4efb4) to head (b28e5c1).

Files with missing lines	Patch %	Lines
petab/v1/distributions.py	84.61%	15 Missing and 5 partials ⚠️
petab/v1/sampling.py	25.00%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #329      +/-   ##
===========================================
- Coverage    74.92%   74.90%   -0.02%     
===========================================
  Files           52       53       +1     
  Lines         4913     5025     +112     
  Branches       845      847       +2     
===========================================
+ Hits          3681     3764      +83     
- Misses         923      947      +24     
- Partials       309      314       +5     

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