refactor: Simplify ApplyStats and ApplyHash

Summary:
This is a backport of core#19521 [3/17]
https://github.com/bitcoin/bitcoin/pull/19521/commits/a8a46c4b3cfda4b95c92a36f8cebd3606377e57d

Depends on D11596

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11597