santad: use an LRU cache in SNTSyncdQueue #344
Description
#341 moves SNTSyncdQueue from NSCache to SantaCache, this is a better fit, but not a perfect fit. An LRU would be more appropriate, frequently blocked executions should stay in the cache vs. being evicted when the cache fills up.
Once we decided on an LRU for Santa's codebase, switch to an LRU in SNTSyncdQueue.