[net processing] Move block cache state into PeerManagerImpl

Summary:
Also make most_recent_block_hash a BlockHash

This is a partial backport of core#24543
https://github.com/bitcoin/bitcoin/pull/24543/commits/10b83e2aa3393ef2c942fde7ac86e8cf3ea224c1

Depends on D14863

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14864