Refactored methods/properties for constructing URLs in the API

[mesozoic]

This branch replaces the hodgepodge of something_url() methods on various classes with a .urls property that can contain both 'hardcoded' URLs (which are only calculated once per object) and URL-returning methods. It simplifies the namespace of each containing object and makes it clearer how to add more URLs in the future for any more API endpoints we need.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3dc0d35) to head (ec52015).

Additional details and impacted files

@@            Coverage Diff             @@
##              main      #399    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           27        27            
  Lines         3135      3242   +107     
==========================================
+ Hits          3135      3242   +107     

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