Instrumenting Caffeine

The metrics-caffeine module provides MetricsStatsCounter, a metrics listener for Caffeine caches:

LoadingCache<Integer, Integer> cache = Caffeine.newBuilder()
    .recordStats(() -> new MetricsStatsCounter(registry, "cache"))
    .build(key -> key);

The listener publishes these metrics:

`hits`	Number of times a requested item was found in the cache.
`misses`	Number of times a requested item was not found in the cache.
`loads-success`	Timer for successful loads into cache.
`loads-failure`	Timer for failed loads into cache.
`evictions`	Histogram of eviction weights .
`evictions-weight`	Total weight of evicted entries.
`evictions.<CAUSE>`	Histogram of eviction weights for each RemovalCause