InMemoryEntityCache is uninstrumented (JDBC persistence)

### Is your feature request related to a problem? Please describe.

I would like to be able to tune the entity cache weighter configuration according to observed statistics.

### Describe the solution you'd like

Wire through Caffeine stats as well as any additional stats that might be useful, analogous to those in the NoSQL [CaffeineCacheBackend](https://github.com/apache/polaris/blob/7866ce5c009d64e4c1454b47bca3df9873c6c0b2/persistence/nosql/persistence/impl/src/main/java/org/apache/polaris/persistence/nosql/impl/cache/CaffeineCacheBackend.java) class.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start with the JDBC persistence implementation and locate InMemoryEntityCache. Compare its available cache behavior with persistence/nosql/persistence/impl/src/main/java/org/apache/polaris/persistence/nosql/impl/cache/CaffeineCacheBackend.java, then identify the Caffeine and other useful statistics to expose. Done means the JDBC cache provides analogous observable statistics for tuning its weighter configuration.

Written by the indexing model from the issue text.