[avalanche] Add a ValidationState for Proof

Summary:
This reproduce the same patern we use to validate transactions and blocks.

It's a useful pattern, because we can test why the check failed exactly.

Test Plan:

ninja all check-avalanche

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6962