TTL this cache enforces, in milliseconds.
Remove every entry.
Live entries sorted by cache key (deterministic ordering).
Look up a single neighbor by MAC (case-insensitive); skips expired ones.
Live neighbors sorted by cache key (deterministic ordering).
Record a freshly decoded neighbor. Upserts by mndpNeighborKey,
refreshing lastSeenAt and replacing the stored announcement. Returns the
resulting entry.
Drop expired entries; returns the number removed.
Number of non-expired entries currently held.
A neighbor cache that expires entries TTL ms after they were last seen.