Build query cache for regexes
Use `r_sanity_check` instead of `guarantee`.
Add LRU cache class.
Use LRU cache for eviction.
Mark as explicit
Address picayune review details
Adjust ampersand position
Describe where I got the value for the LRU cache size from.
Merge branch 'gchpaco_2196' into next

Hopefully fixes #2196.  Code Review was 2072.