Fix custom exceptions to preserve messages

[drbenvincent]

Summary

• Call super().__init__(message) in custom exceptions while preserving self.message.
• Add regression tests for exception string rendering.

Testing

• conda run -n CausalPy python -m pytest (fails: PyTensor compiledir permission error)
• PYTENSOR_FLAGS="compiledir=/tmp/pytensor" conda run -n CausalPy python -m pytest (timed out at 120s)

Closes #665

[read-the-docs-community]

Documentation build overview

📚 causalpy | 🛠️ Build #31244666 | 📁 Comparing b08240e against latest (2cf6d3a)

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Show files changed (23 files in total): 📝 23 modified | ➕ 0 added | ➖ 0 deleted

File	Status
404.html	📝 modified
api/generated/causalpy.pymc_models.BayesianBasisExpansionTimeSeries.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.BayesianBasisExpansionTimeSeries.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.InstrumentalVariableRegression.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.InstrumentalVariableRegression.predict.html	📝 modified
api/generated/causalpy.pymc_models.InstrumentalVariableRegression.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.LinearRegression.build_model.html	📝 modified
api/generated/causalpy.pymc_models.LinearRegression.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.LinearRegression.predict.html	📝 modified
api/generated/causalpy.pymc_models.LinearRegression.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.PropensityScore.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.PropensityScore.predict.html	📝 modified
api/generated/causalpy.pymc_models.PropensityScore.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.PyMCModel.build_model.html	📝 modified
api/generated/causalpy.pymc_models.PyMCModel.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.PyMCModel.predict.html	📝 modified
api/generated/causalpy.pymc_models.PyMCModel.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.StateSpaceTimeSeries.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.StateSpaceTimeSeries.priors_from_data.html	📝 modified
api/generated/causalpy.pymc_models.WeightedSumFitter.build_model.html	📝 modified
api/generated/causalpy.pymc_models.WeightedSumFitter.calculate_cumulative_impact.html	📝 modified
api/generated/causalpy.pymc_models.WeightedSumFitter.predict.html	📝 modified
api/generated/causalpy.pymc_models.WeightedSumFitter.priors_from_data.html	📝 modified

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.36%. Comparing base (2cf6d3a) to head (b08240e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #695   +/-   ##
=======================================
  Coverage   94.35%   94.36%           
=======================================
  Files          44       45    +1     
  Lines        7517     7527   +10     
  Branches      456      456           
=======================================
+ Hits         7093     7103   +10     
  Misses        262      262           
  Partials      162      162           

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