utils: BoundedLRUCache performance improvements

* Add a JRuby-only implementation which delegates the backing map to LinkedHashMap.
  This reduces the critical section in Ruby, micro-benchmarking it shows a speed
  improvement of 40%
* Bump the default max_size value to 10k, to reduce the rate of deletes

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>