Remove `<BLANKLINE>` from docstrings

[drbenvincent]

• Removes a bunch of <BLANKLINE> instances in the docstrings. They were put there in #330 in order to fix failing tests. And that was happening because the progress bar was misbehaving.
• This was fixed in https://github.com/pymc-devs/pymc/pull/7290 so we no longer need most <BLANKLINE> instances.
• This PR removes those, and increments the required version of PyMC to 5.15.1 which is the version to include https://github.com/pymc-devs/pymc/pull/7290
• Closes #331
• This should also fix failing remote tests that we are seeing in other PR's.

[codecov[bot]]

Codecov Report

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

Project coverage is 79.98%. Comparing base (040f20d) to head (298deb1).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #346 +/- ## ========================================== - Coverage 80.12% 79.98% -0.14% ========================================== Files 21 21 Lines 1650 1634 -16 ========================================== - Hits 1322 1307 -15 + Misses 328 327 -1 ```

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