join method
Waits for the Isolate to complete execution.
Equivalent to Java's thread.join(). Returns a Future that completes
when the Isolate sends a 'done' signal or terminates.
Throws InvalidArgumentException if called before start().
Example:
await thread.join();
Implementation
Future<void> join() {
if (_joinCompleter == null) {
throw InvalidArgumentException('DartThread has not been started.');
}
return _joinCompleter!.future;
}