Enable multiple treated units in synthetic control quasi experiments

[drbenvincent]

Closes #456

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📚 Documentation preview 📚: https://causalpy--494.org.readthedocs.build/en/494/

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Codecov Report

Attention: Patch coverage is 98.50374% with 6 lines in your changes missing coverage. Please review.

Project coverage is 95.13%. Comparing base (632c457) to head (25608ef).

Files with missing lines	Patch %	Lines
causalpy/tests/test_pymc_models.py	98.20%	3 Missing ⚠️
causalpy/pymc_models.py	95.74%	2 Missing ⚠️
causalpy/experiments/synthetic_control.py	97.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #494      +/-   ##
==========================================
+ Coverage   94.59%   95.13%   +0.54%     
==========================================
  Files          28       28              
  Lines        2053     2384     +331     
==========================================
+ Hits         1942     2268     +326     
- Misses        111      116       +5     

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[drbenvincent]

Note to self

Relatively happy with where this is at now.

I should do more manual inspection of the tests (which were vibe coded).

There is definitely scope to remove some conditional branching if we set the likelihood of all models to be 1 dimensions. So it would change from (n_obs,) and turn into (n_obs,1). But I think I'll leave that for another PR potentially.

[Copilot]

Pull Request Overview

This PR enables handling multiple treated units throughout the synthetic control workflow by updating documentation, extending the PyMC models, and adding comprehensive multi-unit tests.

• Added sphinx-togglebutton for interactive docs
• Extended PyMCModel and WeightedSumFitter to accept and process multiple treated units
• Updated SyntheticControl class and added end-to-end tests for multi-unit scenarios

Reviewed Changes

Copilot reviewed 6 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pyproject.toml	Added sphinx-togglebutton to docs dependencies
docs/source/conf.py	Registered sphinx_togglebutton extension
causalpy/tests/test_pymc_models.py	Added fixtures and tests for multi-unit WeightedSumFitter
causalpy/tests/test_integration_pymc_examples.py	Added fixtures and integration tests for multi-unit SyntheticControl
causalpy/pymc_models.py	Updated _data_setter, predict, score, and coefficient printing to support multi-unit
causalpy/experiments/synthetic_control.py	Renamed dims (control_units → coeffs), parameterized plots and data getters for treated units

[drbenvincent]

That last commit was quite a big one. Model likelihoods are now 2-dimensional. This means we can avoid a lot of conditional branching based on single vs multiple treated unit situations.