Add support for Sendable types to allow projects that use Swift 6 to consume this library

[edorphy]

Hey Antoine,

This package could use an update to support sendable network types for Swift 6 structured concurrency compliance and compatibility.

Making a simple API call will be prohibited if the project is fully Swift 6.

Thoughts on:

• Updating the Package.swift with Swift 6.0 tools
• Adding Sendable conformance to the model types
• Addressing other issues along the way