Optimized storage lookups for side nodes in the SMT (#784)

* Optimized storage lookups for side nodes in the SMT

* Updated CHANGELOG.md

* Make clippy happy

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - [#781](https://github.com/FuelLabs/fuel-vm/pull/781): Added `base_asset_id` to checked metadata.
 
 ### Changed
+- [#784](https://github.com/FuelLabs/fuel-vm/pull/784): Avoid storage lookups for side nodes in the SMT.
 - [#787](https://github.com/FuelLabs/fuel-vm/pull/787): Fixed charge functions to profile cost before charging.
 
 #### Breaking
@@ -24,6 +25,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - [#786](https://github.com/FuelLabs/fuel-vm/pull/786): Fixed the CCP opcode to charge for the length from the input arguments.
 - [#785](https://github.com/FuelLabs/fuel-vm/pull/785): Require `ContractCreated` output in the `Create` transaction. The `TransactionBuilder<Create>` has a `add_contract_created` method to simplify the creation of the `ContractCreated` output for tests.
 
+
 ## [Version 0.54.1]
 
 ### Changed

fuel-merkle/src/common/node.rs

@@ -24,13 +24,20 @@ pub trait Node {
 
 pub trait ParentNode: Sized + Node {
     type Error;
+    type ChildKey;
 
+    fn key(&self) -> Self::ChildKey;
     fn left_child(&self) -> ChildResult<Self>;
+    fn left_child_key(&self) -> ChildKeyResult<Self>;
     fn right_child(&self) -> ChildResult<Self>;
+    fn right_child_key(&self) -> ChildKeyResult<Self>;
 }
 
 #[allow(type_alias_bounds)]
 pub type ChildResult<T: ParentNode> = Result<T, ChildError<T::Key, T::Error>>;
+#[allow(type_alias_bounds)]
+pub type ChildKeyResult<T: ParentNode> =
+    Result<T::ChildKey, ChildError<T::Key, T::Error>>;
 
 #[derive(Debug, Clone, derive_more::Display)]
 pub enum ChildError<Key, E>