feat: pass Decodable struct to flag evaluation

[nicklasl]

This PR introduces

a significant enhancement to the Confidence SDK for Swift by adding support for passing Decodable structs directly to flag evaluation. The main changes include:

API Methods:

• Updated getEvaluation<T: Decodable>(key: String, defaultValue: T) method that allows passing a Codable struct as context
• Updated getValue<T: Decodable>(key: String, defaultValue: T) method for direct value retrieval with context

Type Safety:

This provides better compile-time checking and IDE support compared to the dictionary-based approach

Backward Compatibility:

All existing methods continue to work as before since ConfidenceValue's are Codeable.

This enhancement makes the SDK more Swift-idiomatic by:

• Leveraging Swift's type system more effectively
• Providing better developer experience with compile-time type checking
• Making it easier to work with structured data in flag evaluations
• Reducing the need for manual conversion between structs and dictionaries

The changes are particularly useful for developers who want to:

• Pass strongly-typed context data to flag evaluations
• Work with complex data structures in their flag evaluations
• Maintain type safety throughout their flag evaluation code

Open questions

• How do we handle when there's a mis match between flag struct and the decodable struct?