Add unit tests for ProtectEvictionCandidatesByRatio()
Add unit tests for ProtectEvictionCandidatesByRatio()

Summary:
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/20197 | core#20197]] [4/6]
https://github.com/bitcoin/bitcoin/pull/20197/commits/72e30e8e03f880eba4bd1c3fc18b5558d8cef680

Depends on D10977

Test Plan: `ninja check`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10978

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