Refactor: Add method to SMT node to set prefix (#70)

* Minor SMT node refactor

* Undo assert change

fuel-merkle/src/sparse/node.rs

@@ -34,7 +34,7 @@ impl Node {
  let buffer = Self::default_buffer();
  let mut node = Self { buffer };
  node.set_height(0);
- node.set_bytes_prefix(&[LEAF]);
+ node.set_prefix(LEAF);
  node.set_bytes_lo(key);
  node.set_bytes_hi(&sum(data));
  node
@@ -44,7 +44,7 @@ impl Node {
  let buffer = Self::default_buffer();
  let mut node = Self { buffer };
  node.set_height(left_child.height() + 1);
- node.set_bytes_prefix(&[NODE]);
+ node.set_prefix(NODE);
  node.set_bytes_lo(&left_child.hash());
  node.set_bytes_hi(&right_child.hash());
  node
@@ -75,6 +75,11 @@ impl Node {
  self.bytes_prefix()[0]
  }
 
+ pub fn set_prefix(&mut self, prefix: u8) {
+ let bytes = prefix.to_be_bytes();
+ self.set_bytes_prefix(&bytes);
+ }
+
  pub fn leaf_key(&self) -> &Bytes32 {
  assert!(self.is_leaf());
  self.bytes_lo().try_into().unwrap()