GQ compatibility with all fitted model objects

[jgabry]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

• Closes generate_quantities should support mle, pathfinder, and laplace objects as input #1203
• Should be merged after add generate_quantities timing support #1168

generate_quantities() now accepts all fitted model objects as input to the fitted_params argument.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Jonah Gabry

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.48%. Comparing base (e27a88f) to head (5db56e4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1204      +/-   ##
==========================================
+ Coverage   90.64%   91.48%   +0.83%     
==========================================
  Files          15       15              
  Lines        6149     6155       +6     
==========================================
+ Hits         5574     5631      +57     
+ Misses        575      524      -51     

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