@TinyStorageItemSet: New property wrapper to retrieve from all keys of a type, as a dictionary

[Mohamad-Kredly]

Use case

Having a String enum conforming to TinyStorageKey, I wanted to access all of the stored value for the possible keys in one place instead of having to use a TinyStorageItem wrapper for every case and possibly miss some as I update the code.

What's new

This PR introduces two main things:

• TinyStorageBuildableKey: Protocol to initialize a conforming type from a String raw value, if possible.
• @TinyStorageItemSet: A property wrapper for a dictionary of Key conforming to the a new protocol and Type of Codable, Sendable, and Equatable. Note that String is not supported as a key as it would include all possible keys which goes against the use case described here.

Updates to README:

• Added the new PropertyWrapper to the Usage section.
• "Migration from UserDefaults" has been moved to its own section.

Usage

@TinyStorageItemSet(storage: .appGroup)
var platformStates: [Platform: AuthorizationState] = [.discord: .signedOut]

var body: some View {
    VStack {
        ForEach(Array(platformStates.keys)) { platform in
            Text("Platform \(platform.rawValue) is \(platformStates[platform]?.rawValue ?? "unset")")
        }
    }
}

public enum Platform: String, Identifiable, Codable, Sendable, TinyStorageBuildableKey  {
    case discord
    case twitter
    case bluesky
    
    public var id: String {
        self.rawValue
    }
}

public enum AuthorizationState: String, Codable, Sendable {
    case notDetermined
    case restricted
    case signedIn
    case signedOut
}

[christianselig]

Very cool idea! I'm gonna leave this up as a PR because it feels slightly out of scope of what I'm envisioning for this library, but leaving it up as I think this is a cool use case that someone else may benefit from! Great work

[Mohamad-Kredly]

Thanks!