[feature] Refactor C3Options for Improved Structure and Maintainability

[Meow404]

Description

The C3Options struct in c3_options.h is functional but can benefit from a structural refactor to improve readability, maintainability, and scalability. Currently, the struct contains a large number of parameters, some of which are loosely related, making it harder to navigate and understand. By introducing sub-structs, enumerations, and grouping related parameters, we can simplify the organization and enhance the usability of the code.

2. Use Enumerations for Fixed Options:

   • Replace string-based parameters like contact_model and projection_type with enumerations for type safety and clarity:

     enum class ContactModel { StewartAndTrinkle, Anitescu };
     enum class ProjectionType { QP, MIQP };

3. Encapsulate Cost Matrix Parameters:

   • Move cost matrix parameters (Q, R, G, U, and their scaling factors) into a dedicated sub-struct for better modularity.

4. Improve Serialization Logic:

   • Simplify the Serialize method by delegating serialization to sub-structs, reducing redundancy and improving readability.

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Advantages of the Refactor

1. Improved Readability:

   • Grouping related parameters makes the code easier to navigate and understand.
   • Enumerations provide clear, self-documenting code.

2. Enhanced Maintainability:

   • Changes to specific parameter groups (e.g., cost matrices) can be made in isolation without affecting unrelated parts of the struct.

3. Type Safety:

   • Enumerations prevent invalid values (e.g., typos in strings like "stewart_and_trinkle") and ensure only valid options are used.

4. Scalability:

   • Adding new parameters or features becomes easier without bloating the main struct.

5. Cleaner Serialization:

   • Delegating serialization to sub-structs reduces duplication and makes the logic more modular.

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[Meow404]

TODO: Possibly add handling for Solver Options as well eg. OSQP solver options