Fix circular import

[AaronDJohnson]

This pull request fixes a circular import by moving CompareTimingModels to timing.py and removing import models from model_utils.py.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 11.94030% with 59 lines in your changes missing coverage. Please review.

Project coverage is 37.29%. Comparing base (d91baf2) to head (03b1ab4).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
enterprise_extensions/timing.py	11.94%	59 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #244   +/-   ##
=======================================
  Coverage   37.29%   37.29%           
=======================================
  Files          20       20           
  Lines        3974     3974           
=======================================
  Hits         1482     1482           
  Misses       2492     2492           

Files with missing lines	Coverage Δ
enterprise_extensions/model_utils.py	14.01% <ø> (+0.61%)	⬆️
enterprise_extensions/timing.py	15.90% <11.94%> (-12.67%)	⬇️

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