🏛️ Architect: Extract generic optimization module

[fderuiter]

This PR performs a "Module Extraction" refactoring by moving the mathematical implementation of optimization algorithms (SGD, Adam) from the AI-specific modules (ai::optimization, ai::sds::training) to a new, generic pure_math::optimization module.

Changes:

1. New Module: math_explorer/src/pure_math/optimization.rs defines a generic Optimizer<P> trait and implements SGD and Adam structs that work with nalgebra types (DMatrix, DVector).
2. Refactoring: math_explorer/src/ai/optimization.rs now delegates the mathematical updates to the new module, while maintaining its layer-based state management logic.
3. Cleanup: Duplicate implementations in math_explorer/src/ai/sds/training.rs were removed and replaced with the core primitives.
4. Verification: All tests passed (cargo test pure_math::optimization, cargo test ai).

Impact:

• Reduces code duplication.
• Decouples optimization logic from neural network topology.
• Makes optimization algorithms reusable for other domains (e.g., Physics simulations, Curve fitting).

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PR created automatically by Jules for task 8598226063567658698 started by @fderuiter

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