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?

[rokridi]

I think that func asJSONData() -> Data? could be rewritten like this:

public extension ConfidenceValue {
    func asJSONData() -> Data? {
        return try? JSONSerialization.data(withJSONObject: self.value.jsonValue)
    }
}

extension ConfidenceValueInternal {
    var jsonValue: Any {
        return switch self {
        case .boolean(let bool):
            bool
        case .string(let string):
            string
        case .integer(let int):
            int
        case .double(let double):
            double
        case .date(let dateComponents):
            dateComponents
        case .timestamp(let date):
            date
        case .list(let array):
            array.map(\.jsonValue)
        case .structure(let dictionary):
            dictionary.mapValues(\.jsonValue)
        case .null:
            NSNull()
        }
    }
}