Add PartialEq to BoundKind and Value

Implement PartialEq for BoundKind to allow for structural equality
checks during optimization. This enables the optimizer to terminate
early when a node no longer changes.

Also, implement PartialEq for Value to facilitate comparisons between
different Value variants.

src/ast/nodes.rs

@@ -25,7 +25,7 @@ impl From<&str> for Symbol {
 }
 
 /// A generic AST Node wrapper to preserve identity and metadata
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Node<K, T = ()> {
     pub identity: Identity,
     pub kind: K,