Faster BeaconState enc/dec (#671)

* Add state enc/dec benches

* Add example for flamegraph

* Use `PublicKeyBytes` for `Validator`

* Ripple PublicKeyBytes change through codebase

* Add benches, optimizations to store BeaconState

* Store BeaconState in StorageContainer too

* Optimize StorageContainer with std::mem magic

* Fix rest_api tests

eth2/types/examples/ssz_encode_state.rs

@@ -0,0 +1,50 @@
+//! These examples only really exist so we can use them for flamegraph. If they get annoying to
+//! maintain, feel free to delete.
+
+use ssz::{Decode, Encode};
+use types::{
+    test_utils::generate_deterministic_keypair, BeaconState, Eth1Data, EthSpec, Hash256,
+    MinimalEthSpec, Validator,
+};
+
+type E = MinimalEthSpec;
+
+fn get_state(validator_count: usize) -> BeaconState<E> {
+    let spec = &E::default_spec();
+    let eth1_data = Eth1Data {
+        deposit_root: Hash256::zero(),
+        deposit_count: 0,
+        block_hash: Hash256::zero(),
+    };
+
+    let mut state = BeaconState::new(0, eth1_data, spec);
+
+    for i in 0..validator_count {
+        state.balances.push(i as u64).expect("should add balance");
+        state
+            .validators
+            .push(Validator {
+                pubkey: generate_deterministic_keypair(i).pk.into(),
+                withdrawal_credentials: Hash256::from_low_u64_le(i as u64),
+                effective_balance: i as u64,
+                slashed: i % 2 == 0,
+                activation_eligibility_epoch: i.into(),
+                activation_epoch: i.into(),
+                exit_epoch: i.into(),
+                withdrawable_epoch: i.into(),
+            })
+            .expect("should add validator");
+    }
+
+    state
+}
+
+fn main() {
+    let validator_count = 1_024;
+    let state = get_state(validator_count);
+
+    for _ in 0..1_024 {
+        let state_bytes = state.as_ssz_bytes();
+        let _: BeaconState<E> = BeaconState::from_ssz_bytes(&state_bytes).expect("should decode");
+    }
+}