Port BatchFutures and co.

[rogeralsing]

https://github.com/asynkron/protoactor-dotnet/blob/dev/src/Proto.Actor/Future/FutureBatch.cs

FutureBatch is a special Future that registers into the ProcessRegistry, and then allows requests to re-use this future but with a unique request-id per request.

[rogeralsing]

This is less critical than other features. but still a nice perf optimization