Add a optional parameter 'waitAll' on combineLatestAll

[tpouriel]

Allow combineLastestAll output stream to emit events even if all the input streams don't have emitted yet.

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[tpouriel]

I can provide more tests, docs and bump version if this base modification looks good to you...

[natebosch]

Can you describe your use case?

[tpouriel]

My usecase is the following : I have a source stream emitting events describing the state of a model in a database. The stream is consumed by a consumer, typically a Widget. In between I have a some "middlewares" that inject more stuff into the model, but some of the middleware can be quite slow if they have a lot of computation.

Here is what it looks like :

class Model {
...
}

interface Producer {
   Stream<List<Model>> streamFromDb();
}

interface Middleware {
   Stream<List<Model>> applyModification(Stream<List<Model>> source);
}

class StreamManager {
   final List<Middleware> middlewares = [...];
   final Producer producer;
   
   Stream<List<Model>> getAugmentedStream() {
      final source = producer.streamFromDb().asBroadcastStream();
     return middlewares.first.applyModification(source).combineLatestAll(middlewares.subList(1).map((middleware) => middleware.applyModification(source)).map(_resolveModifications);
   }
}

interface Consumer  {
   // getAugmentedStream is called here
}