Fix ModifiedBetaGeoNBDRV sim_data

[PabloRoque]

Description

Fixes sim_data in ModifiedBetaGeoNBDRV

• Pre-fix behavior: pm.sample_prior_predictive | pm.sample_posterior_predictive would return 0 for recency | frequency vars.
• Post-fix behavior: both methods return correct samples.

See lifetimes implementation for reference

Related Issue

• Closes #
• Related to Allow plot_expected_purchases_pcc in BetaGeoModel and ModifiedBetaGeoModel #1470

Checklist

• Checked that the pre-commit linting/style checks pass. Feel free to comment pre-commit.ci autofix to auto-fix.
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks) using numpydoc format.
• If you are a pro: each commit corresponds to a relevant logical change

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📚 Documentation preview 📚: https://pymc-marketing--1472.org.readthedocs.build/en/1472/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.55%. Comparing base (4ef55f3) to head (12fac44).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1472   +/-   ##
=======================================
  Coverage   92.55%   92.55%           
=======================================
  Files          52       52           
  Lines        5947     5947           
=======================================
  Hits         5504     5504           
  Misses        443      443           

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[PabloRoque]

Triggered pre-commit.ci - pr 3 times, but it keeps failing... Issues with mypy build timing out.