[avalanche] Add a way to promote old entries in the contender cache to a new chain tip

Summary: Remote proofs are only tracked by proofid in the peer manager, so the contender cache needs to continuously "promote" cache entries since it does not store the proofs themselves. Each time promotion is attempted, an indirect validity check is done to ensure the cache is not tracking invalid proofs.

Test Plan:

ninja check-avalanche-stakecontendercache_tests

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16951