cmd, core, eth, light, trie: add trie read caching layer

vendor/github.com/allegro/bigcache/stats.go

@@ -0,0 +1,15 @@
+package bigcache
+
+// Stats stores cache statistics
+type Stats struct {
+	// Hits is a number of successfully found keys
+	Hits int64 `json:"hits"`
+	// Misses is a number of not found keys
+	Misses int64 `json:"misses"`
+	// DelHits is a number of successfully deleted keys
+	DelHits int64 `json:"delete_hits"`
+	// DelMisses is a number of not deleted keys
+	DelMisses int64 `json:"delete_misses"`
+	// Collisions is a number of happened key-collisions
+	Collisions int64 `json:"collisions"`
+}