Improve Empty response handling in Either and Domain implementations

[LuisAlvarez5]

Improve Empty response handling in Either and Domain implementations

This commit enhances the way to handle empty responses, particularly for Either types.

Key Changes:

• Implement type-safe Either response checking using EitherCheckable protocol
• Replace string-based type checking with Swift's native type system
• Add safe empty JSON data handling without force unwrapping
• Unify empty response handling for both Empty and Either<Empty, ErrorResponse> types
• Improve decoder implementation to handle empty responses consistently

Technical Details:

• Add EitherCheckable protocol for type-safe Either response type inspection
• Implement static responseType property to access generic type information
• Add safe initialization for empty JSON data
• Consolidate empty response handling logic in Domain.perform

[markiv]

static let emptyJsonData = Data("{}".utf8)