refactor priors

[hillalex]

• no need for a base class of guassian priors
• change weird function signature from 2 vectors to just named arguments

(this will help with the interactive shiny app, but also just make sense, the current interface is weird for no reason)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.54%. Comparing base (edeefbb) to head (85979fc).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
+ Coverage   93.47%   93.54%   +0.07%     
==========================================
  Files           9        9              
  Lines         506      496      -10     
==========================================
- Hits          473      464       -9     
+ Misses         33       32       -1     

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