Fix Shard failed to unwrap buffered messages correctly

[Arkatufus]

Changes

• Change Shard ctor to accept buffer message adapter
• Add reproduction test

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• This change follows the Akka.NET API Compatibility Guidelines.
• This change follows the Akka.NET Wire Compatibility Guidelines.
• I have reviewed my own pull request.

[Aaronontheweb]

Related: petabridge/phobos-issues#84

[Aaronontheweb]

Need to re-arrange the reproduction - don't do anything custom inside the HashCodeMessageExtractor. Handle this in the Unapply method instead.

[Aaronontheweb]

This is kind of testing the wrong thing here - the Unapply method should be handling this.

[Arkatufus]

no its not, we're testing MyEnvelope, that Message class is the actual message being sent, not a string.

[Arkatufus]

actually, you're right, there's something wrong with the repro code