Refactor biology module: Replace panics with Result and enforce safety

[fderuiter]

• Introduced DiffusionError, SpatialDiffusionError, and MorphogenesisError using thiserror.
• Updated DiffusionModel, SpatialDiffusion, and TuringSolverStrategy traits to return Result.
• Updated FiniteDifference1D, FiniteDifference2D, and FusedEulerSolver to return proper errors on dimension mismatches instead of panicking or failing silently.
• Updated TuringSystem::step to return Result.
• Updated usage in OdeSystem::derivative_in_place implementations to expect success (maintaining trait contract).
• Cleaned up unused imports and variables in several modules to address warnings.
• Verified with cargo test and cargo check.

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PR created automatically by Jules for task 17291833803350719285 started by @fderuiter

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