Mock posterior with prior on various CLV tests

[wd60622]

I've mocked the posterior sampling with the sample_prior_predictive for handful of the CLV tests that only check for input and output.
For instance, save and load. Should shave off some time in the CI

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📚 Documentation preview 📚: https://pymc-marketing--1156.org.readthedocs.build/en/1156/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.61%. Comparing base (7a84c64) to head (ba679f9).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1156   +/-   ##
=======================================
  Coverage   95.61%   95.61%           
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  Files          39       39           
  Lines        4063     4063           
=======================================
  Hits         3885     3885           
  Misses        178      178           

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[juanitorduz]

LGTM :)

[ColtAllen]

Thanks for speeding up the tests! Couldn't get around to reviewing this today, but these new test methods may be useful for my ongoing plotting PR.