Optimizations, disable val client sync check & additional lcli tools (#834)

* Start adding interop genesis state to lcli

* Use more efficient method to generate genesis state

* Remove duplicate int_to_bytes32

* Add lcli command to change state genesis time

* Add option to allow VC to start with unsynced BN

* Set VC to do parallel key loading

* Don't default to dummy eth1 backend

* Add endpoint to dump operation pool

* Add metrics for op pool

* Remove state clone for slot notifier

* Add mem size approximation for tree hash cache

* Avoid cloning tree hash when getting head

* Fix failing API tests

* Address Michael's comments

* Add HashMap::from_par_iter

eth2/types/src/beacon_state.rs

@@ -97,6 +97,21 @@ impl BeaconTreeHashCache {
     pub fn is_initialized(&self) -> bool {
         self.initialized
     }
+
+    /// Returns the approximate size of the cache in bytes.
+    ///
+    /// The size is approximate because we ignore some stack-allocated `u64` and `Vec` pointers.
+    /// We focus instead on the lists of hashes, which should massively outweigh the items that we
+    /// ignore.
+    pub fn approx_mem_size(&self) -> usize {
+        self.block_roots.approx_mem_size()
+            + self.state_roots.approx_mem_size()
+            + self.historical_roots.approx_mem_size()
+            + self.validators.approx_mem_size()
+            + self.balances.approx_mem_size()
+            + self.randao_mixes.approx_mem_size()
+            + self.slashings.approx_mem_size()
+    }
 }
 
 /// The state of the `BeaconChain` at some slot.
@@ -996,6 +1011,12 @@ impl<T: EthSpec> BeaconState<T> {
             tree_hash_cache: BeaconTreeHashCache::default(),
         }
     }
+
+    pub fn clone_with_only_committee_caches(&self) -> Self {
+        let mut state = self.clone_without_caches();
+        state.committee_caches = self.committee_caches.clone();
+        state
+    }
 }
 
 impl From<RelativeEpochError> for Error {