perf(imt): when updating a node, skip calculation if value is the same

In order to improve performance, we can avoid recalculating the Incremental Merkel Tree in the event
that the update value is the same as the tree value.

re #340

packages/imt/src/imt.ts

@@ -224,6 +224,8 @@ export default class IMT {
             throw new Error("The leaf does not exist in this tree")
         }
 
+        if (newLeaf === this._nodes[0][index]) return
+
         let node = newLeaf
 
         for (let level = 0; level < this.depth; level += 1) {

packages/imt/tests/imt.test.ts

@@ -131,6 +131,25 @@ describe("IMT", () => {
                         expect(tree.root).toEqual(root)
                     }
                 })
+
+                it(`Should not error when update value is the same`, () => {
+                    for (let i = 0; i < numberOfLeaves; i += 1) {
+                        tree.insert(1)
+                        oldTree.insert(1)
+                    }
+
+                    const previousRoot = tree.root
+
+                    for (let i = 0; i < numberOfLeaves; i += 1) {
+                        tree.update(i, 1)
+                        oldTree.update(i, 1)
+
+                        const { root } = oldTree.genMerklePath(0)
+
+                        expect(tree.root).toEqual(root)
+                        expect(tree.root).toEqual(previousRoot)
+                    }
+                })
             })
 
             describe("# indexOf", () => {