net: Add unit testing of node eviction logic

Summary:
Backport of core#20477.

Depends on D9683.

Ref T1611.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1611

Differential Revision: https://reviews.bitcoinabc.org/D9684