Evaluate replacing ristretto with theine-go

[jzelinskie]

Problem Statement

Ristretto is non-ideal for a bunch of reasons:

• Ristretto is somewhat unmaintained; there are some ex-dgraph folks under the organization outcaste-io triaging but not actively developing.
• Major users like Vitess have replaced it.
• I've now seen both the theine and otto developers very much so struggle to reproduce ristretto's benchmarks leading me to believe our usage could also be misconfigured leading to significantly worse performance. This comment recently caught my attention
• Ristretto doesn't support Go's generics
• Ristretto doesn't implement all of the things that make Caffeine (the premier java tinylfu implementation) perform optimally

Solution Brainstorm

Support theine or otto using our cache interface and a hidden feature flag until we can confirm performance and deprecate ristretto