Add LRU cache to database (#837)

* Add LRU caches to store

* Improvements to LRU caches

* Take state by value in `Store::put_state`

* Store blocks by value, configurable cache sizes

* Use a StateBatch to efficiently store skip states

* Fix store tests

* Add CloneConfig test, remove unused metrics

* Use Mutexes instead of RwLocks for LRU caches

beacon_node/beacon_chain/src/eth1_chain.rs

@@ -883,7 +883,7 @@ mod test {
                     &state
                         .get_state_root(prev_state.slot)
                         .expect("should find state root"),
-                    &prev_state,
+                    prev_state,
                 )
                 .expect("should store state");
 
@@ -953,7 +953,7 @@ mod test {
                     &state
                         .get_state_root(Slot::new(0))
                         .expect("should find state root"),
-                    &prev_state,
+                    prev_state,
                 )
                 .expect("should store state");