Standardize plot theming across tutorials

[cdc-mitzimorris]

• adds file docs/tutorials/_tutorial_theme.py which is included in all tutorials to provide uniform text element sizes across all plots.
• make all plots fill the content column - remove a bunch of figure size controls from individual tutorials also from docs_scripts.
• change plots in docs/tutorials/periodic_effects.qmd to use plotnine.

[cdc-mitzimorris]

@damonbayer - your feedback welcome.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.91%. Comparing base (923fda8) to head (4aaf070).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #713   +/-   ##
=======================================
  Coverage   97.91%   97.91%           
=======================================
  Files          51       51           
  Lines        1580     1580           
=======================================
  Hits         1547     1547           
  Misses         33       33           

Flag	Coverage Δ
unittests	97.91% <ø> (ø)

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[github-actions]

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