test: add testcases for snapshot initialization

Summary:
This is a partial backport of core#25667
https://github.com/bitcoin/bitcoin/pull/25667/commits/e4d799528696c5ede38c257afaffd367917e0de8

Depends on D14654

Test Plan: ninja check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14655