Add enc/decode traits to store

beacon_node/db2/src/impls.rs

@@ -0,0 +1,16 @@
+/*
+use types::*;
+
+impl StoreEncode for Hash256 {
+    fn as_store_bytes(&self) -> Vec<u8> {
+        self.as_bytes().to_vec()
+    }
+}
+
+impl StoreDecode for Hash256 {
+    fn from_store_bytes(bytes: &mut [u8]) -> Vec<u8> {
+        Hash256::from_slice()
+        self.as_bytes().to_vec()
+    }
+}
+*/