[Concurrency] Structured concurrency

[Lantua]

@Sajjon

How do I create my first async method???

The only one I found is Task.withUnsafe(Throwing)Continuation in this pitch.

Task.withUnsafeContinuation { continuation in
  ...
  if ... {
    continuation.resume(returning: returnValue)
  } else {
    continuation.resume(throwing: error)
  }
}