🧱 Mason: Decouple Q-Learning from HashMap storage (Fixes SRP/DIP)

[fderuiter]

🏚️ Violation: The TabularQAgent class mixed two responsibilities: managing the Q-Table storage (using a HashMap) and implementing the Q-Learning update algorithm. This violated the Single Responsibility Principle (SRP) and made it impossible to extend the agent to use other storage mechanisms (like arrays or function approximators) without modifying the core class (violating Open/Closed Principle).

🏗️ Fix:

1. Extracted a QFunction trait in storage.rs to define the interface for getting and setting Q-values.
2. Implemented HashMapQFunction as the default concrete implementation.
3. Refactored TabularQAgent into a generic QAgent<S, A, Q> that depends on the QFunction abstraction.
4. Created a type alias pub type TabularQAgent<S, A> = QAgent<S, A, HashMapQFunction<S, A>>; to ensure backward compatibility for existing code.

🔗 Principle:

• Single Responsibility Principle (SRP): Storage logic is now in HashMapQFunction, learning logic is in QAgent.
• Dependency Inversion Principle (DIP): QAgent depends on the QFunction abstraction, not the concrete HashMap.
• Open/Closed Principle (OCP): New storage backends can be added by implementing QFunction without changing QAgent.

🧪 Verification:

• Ran cargo test --test test_rl which passed.
• The existing tests instantiate TabularQAgent using the legacy constructor, confirming that the type alias and specialized impl block work as expected.

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PR created automatically by Jules for task 8894124242979632810 started by @fderuiter

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