Unify and simplify the deduplication caches

As a preparation to enable better monitoring and add more precise monitoring probes to the deduplication caches I would like to unify their interfaces and simplify their setup.

• Don't expose the cache statistics via the FileStore and leverage the the FileStoreBuilder instead for this.
• All deduplication caches should implement a unified Cache interface to simplify wrapping them (e.g. for additional access statistics collection).
• Replace the ad-hoc collection of cache statistics in the NodeWriteStats inner class of the SegmentWriter and replace it with a more structured approach.
• Expose additional cache access statistics via Metrics.
• The additional statistics should discriminate caches access occurring as regular writes from such occurring during compaction.