* Rewrite cache module in Kotlin.
* Migrate RealStore to use new cache.
* Migrate FileSystemImpl to use new cache.
* Migrate StoreTest to new cache.
* Remove Guava Cache.
* Migrate remaining Java file to Kotlin.
* Fix ktlint error.
* Fix package.
* Add support for CacheLoader.
* Remove unnecessary mockito-inline.
* Remove volatile keyword from CacheEntry fields and add docs re. cache entry reuse and thread-safty assumption.
* - Refactor CacheBuilder.
- Update docs.
- Update Key, Value, Input, Output generic types to be bound by Any.
- Replace spy with TestLoader for asserting invocation.
* Support key-based synchronization for get(key: Key, loader: () -> Value): Value.
* Document loader exception propagation.
* Small clean ups.
* Make CacheEntry's Key and Value bound to Any, move CacheEntry to RealCache.kt as a private class.
* Add reference counting key-based synchronization for cache loader.
* Improve KeyedSynchronizer and docs.
* Refactor tests and add a missing test case to reach 100% coverage.
* Add memory barrier after updating access time in cache entry.
* Only process access queue if expiresAfterAccess == true.
* Support configurable concurrency level.
* Increase delay for concurrency test.
* Explicitly set concurrency level for concurrency tests.
* Only add memory barrier after recordRead if expiresAfterAccess is enabled.
* Fix a potential memory leak caused by thread preemption.
* Allow retries (3 times) for concurrency tests.
* Move performMaintenance function to bottom of the class.
* Fix typos, rename performMaintenance() to cleanUpDeadEntries(), improve docs.
* Fix more typos.
* Only remove entries in map but not in queue.
* Replace memory barrier with @Volatile fields in CacheEntry.
* Fix deadlock while iterating sets.
* Remove stale cache/README.md, remove commented out java file.
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