and an `m_is_onion` struct member to NodeEvictionCandidate and tests.
We'll use these in the peer eviction logic to protect inbound onion peers
in addition to the existing protection of localhost peers.
An unordered set can tell if an element is present in ~O(1) time (constant on
average, worst case linear to the size of the container), which speeds up and
simplifies the lookup in IsEvicted().
Co-authored-by: Vasil Dimov <vd@FreeBSD.org>
out of net_tests, because the eviction tests:
- are a different domain of test coverage, with different dependencies
- run more slowly than the net tests
- will be growing in size, in this PR branch and in the future, as eviction
test coverage is improved
