Refactor distributions

[Andrea-Havron-NOAA]

this PR addesses the following issues:
#170
#573
#581
#585

What is the feature?

• Distribution base was renamed to DensityContributionsBase
• Shared members:
  • observed_values
  • expected_values
  • nll_type
  • osa_flag
  • simulate_flag
• NormalLPDF class
• LognormalLPDF class
• MultinomialLPMF class
• Each child class contains unique class members, evaluate function that loops over observed and expexted values and calculates the nll, simulates and reports observed values

How have you implemented the solution?

Does the PR impact any other area of the project?

The FIMS nll summations will be refactored in the rcpp interface and model.hpp

Output

Itemized nll values are now available

How to test this change

Developer pre-PR checklist

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[github-actions]

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[Andrea-Havron-NOAA]

filed new issue to document files