TransferFeedback for determining if a testcase was from another node

[addisoncrump]

This is useful for short-circuiting potentially expensive objective feedbacks, as well as for creating nodes which just perform analysis on inputs rather than actually fuzzing.

[addisoncrump]

Seeing as how this adds two branches in a non-fast path, I'm going to merge this as is. Revert if there are any major concerns with this change, please.

[tokatoka]

i think this could have been simply a field in Testcase

[domenukk]

Probably a good idea for performance reasons

[addisoncrump]

That doesn't work, because we need this information at evaluation time.

[domenukk]

Then, should be a state-flag in the state?

[addisoncrump]

Potentially so? HasTransferState?

[domenukk]

More a status than a state? State seems a bit overused in a struct called StdState implementing a trait called state :D

[tokatoka]

Let's just allow hooks in handle_in_client?

[domenukk]

sound fun

[tokatoka]

I made a POC in #1916