Improve formatting of model coefficients in `summary` method in pymc-based experiments

[drbenvincent]

Similar to an improvement made in #355 to the summary method in scikit-learn based experiments, but for the pymc based experiments.

Printing of the model coefficients is now better horizontally aligned. The position of the coefficient values is now governed by the width of the longest coefficient label string.

I also re-ran the pymc based notebooks so that we get the updated summary output in the docs.

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📚 Documentation preview 📚: https://causalpy--359.org.readthedocs.build/en/359/

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Codecov Report

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

Project coverage is 83.10%. Comparing base (2916688) to head (267d7c7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #359 +/- ## ========================================== + Coverage 80.87% 83.10% +2.23% ========================================== Files 21 21 Lines 1668 1687 +19 ========================================== + Hits 1349 1402 +53 + Misses 319 285 -34 ```

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