[avalanche] Output a proof registration state

Summary:
This gives extra details on why a proof failed to register. Currently unused, it will be used in various places to improve the error reporting and simplify the code based on what the failure cause is.

Ref T1854.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, tyler-smith

Reviewed By: #bitcoin_abc, tyler-smith

Subscribers: tyler-smith, deadalnix

Maniphest Tasks: T1854

Differential Revision: https://reviews.bitcoinabc.org/D10773