Fix failing doctests

[drbenvincent]

• Closes #323 which is affecting current PR's.
• Also managed to catch a bug where we were not passing in random_seed to pm.sample_posterior_predictive in ModelBuilder.predict. Also replaced a multi-line block with the single line random_seed = self.sample_kwargs.get("random_seed", None) which is much nicer.
• Other than that, the solution was to add varying numbers of <BLANKLINE> to the docstrings. I believe this is because the pymc progress bar is returning empty lines, possibly only in the instance where progressbar=False. I should open an issue in the PyMC repo about that.
• All tests and doctests pass in my local environment, which was build in the conda-based approach, see #304. Remains to be seen if the doctests will pass remotely.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.27%. Comparing base (dbaa17b) to head (8805fb2). Report is 22 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #330 +/- ## ========================================== + Coverage 77.10% 77.27% +0.17% ========================================== Files 21 21 Lines 1380 1395 +15 ========================================== + Hits 1064 1078 +14 - Misses 316 317 +1 ```

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[drbenvincent]

Hurray! Remote tests pass 🎉