feat: add fit_model_flux_to_data function to MSExpression class

- Implements expression-constrained flux balance analysis

- Handles genome-to-model and type transformations
  automatically

- Integrates with ExpressionActivationPkg for optimization

- Includes comprehensive NumPy-style docstring with examples

- Adds 12 unit tests covering all functionality and edge
   cases

- Validates thresholds, conditions, and model compatibility

- Related to PRD 0001 and task list tasks-0001

Author: Christopher Henry