chore: backport LargeSmtForest to 0.19.x branch

[drahnr]

Backport LargeSmt from next to version/0.19.x branch and a few minimal adjacent non-breaking changes, which are limited to mod test_utils addition and a minor extension to SmtLeaf:

diff --git a/miden-crypto/src/merkle/smt/full/leaf.rs b/miden-crypto/src/merkle/smt/full/leaf.rs
index 031ade9a6..3561aa955 100644
--- a/miden-crypto/src/merkle/smt/full/leaf.rs
+++ b/miden-crypto/src/merkle/smt/full/leaf.rs
@@ -175,6 +175,10 @@ impl SmtLeaf {
         self.clone().into_elements()
     }
 
+    pub fn to_entries(&self) -> impl Iterator<Item = (&Word, &Word)> {
+        self.entries().iter().map(|(k, v)| (k, v))
+    }
+
     /// Converts a leaf to a list of field elements
     pub fn into_elements(self) -> Vec<Felt> {
         self.into_entries().into_iter().flat_map(kv_to_elements).collect()
diff --git a/miden-crypto/src/merkle/smt/full/mod.rs b/miden-crypto/src/merkle/smt/full/mod.rs
index 2f2662842..d9b04e4bb 100644
--- a/miden-crypto/src/merkle/smt/full/mod.rs
+++ b/miden-crypto/src/merkle/smt/full/mod.rs
@@ -259,6 +259,11 @@ impl Smt {
         <Self as SparseMerkleTree<SMT_DEPTH>>::get_leaf(self, key)
     }
 
+    /// Returns the leaf corresponding to the provided `index`.
+    pub fn get_leaf_by_index(&self, index: LeafIndex<SMT_DEPTH>) -> Option<SmtLeaf> {
+        self.leaves.get(&index.position()).cloned()
+    }
+
     /// Returns the value associated with `key`
     pub fn get_value(&self, key: &Word) -> Word {
         <Self as SparseMerkleTree<SMT_DEPTH>>::get_value(self, key)

---

Why do we want this backported?

node PR 0xMiden/miden-node#1635 introduces a free-style version of the LargeForestSmt with in Memory backend, using this implementation should lead to easier to maintain code and do away with a lot of (hopefully all) helper lookup tables.

[iamrecursion]

Insofar as this looks like the code I wrote and the fix for truncate is in place, LGTM!