Implement hit-ratio dumping for NotifCollectionCache

This will allow us to keep an eye on whether we end up with too many
cache misses.

Bug: 371174789
Test: NotifCollectionCacheTest for the counters, but the actual printing
isn't tested yet, we can test it manually in a follow-up
Flag: EXEMPT logging only change

Change-Id: Ie7eef8c733ca96c979e2c82b1ca3be3a2a864d8b