Refactor: Enforce Result and Typed Errors in Climate and Clinical Trials

[fderuiter]

This PR refactors the climate and clinical_trials modules to improve error handling and safety.

Key Changes:

1. Climate Module:

   • Added ClimateError enum for structured error handling.
   • Updated mse_loss and earth_movers_distance to return Result instead of panicking on dimension mismatch or invalid data.
   • Updated Cera::new and CeraTrainer::train to propagate errors.
   • Fixed unwrap() usage in earth_movers_distance by using total_cmp.

2. Clinical Trials Module:

   • Updated AllocationStrategy trait to return Result<Vec<Group>, ClinicalTrialError> instead of Result<..., String>.
   • Refactored SimpleRandomizer and BlockRandomizer to implementation this new signature.
   • Kept deprecated functions compatible by mapping errors to String.

These changes eliminate several potential panics and replace "stringly typed" errors with proper Rust error types, aligning with the project's refactoring goals.

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PR created automatically by Jules for task 9569915157609649907 started by @fderuiter

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