refactor: Add SHAMapNodeID::isPrefixOf (#7939)

Co-authored-by: Bart <11445373+bthomee@users.noreply.github.com>

include/xrpl/shamap/SHAMapNodeID.h

@@ -55,6 +55,20 @@ public:
     [[nodiscard]] SHAMapNodeID
     getChildNodeID(unsigned int branch) const;
 
+    /**
+     * Test whether this node ID lies on the path to the given leaf key
+     *
+     * A node at depth d identifies the tree path spelled by the first d
+     * nibbles of its key, so any leaf beneath it must agree on that prefix.
+     * A node ID that fails this test names a different subtree than the one
+     * it was built for.
+     *
+     * @param key  the key of a leaf below this node
+     * @return whether this node ID is a prefix of the leaf key
+     */
+    [[nodiscard]] bool
+    isPrefixOf(uint256 const& key) const;
+
     /**
      * Create a SHAMapNodeID of a node with the depth of the node and
      * the key of a leaf