Implement setting actor metadata with property wrapper fields

[ktoso]

Resolves #479
Resolves #983
Provides a good usability basis for #979

This allows for the following:

    distributed actor Example: CustomStringConvertible {
        typealias ActorSystem = ClusterSystem
        
        @ActorID.Metadata(\.exampleUserID)
        var userID: String

        init(userID: String, actorSystem: ActorSystem) async {
            self.actorSystem = actorSystem
            self.userID = userID
        }
    }

        let userID = "user-1234"
        let example = await Example(userID: userID, actorSystem: system)
        
        example.id.metadata.exampleUserID.shouldEqual(userID)

and replaces our _Props.$forSpawn.withValue(...) { ... } dance.

I've not replaced all the uses of the forSpawn yet, but we should be able to for all DA declarations we have 👍

[yim-lee]

used?

[ktoso]

here yes sadly, just in case™ we use a semaphore here

[ktoso]

@swift-server-bot test this please

[ktoso]

Sigh was happy all day and now a bit flaky...

[ktoso]

Failure is the recently flaky after nio update: #945