Add example and refine local inlining

Add a new example file `examples/def_local_inlining.myc` to demonstrate
and test local inlining.

Refine the optimizer to handle local inlining more robustly by:
- Passing a `SubstitutionMap` to `visit_node` to track local variable
  substitutions.
- Enabling constant propagation for local variables by checking
  `sub.locals` in `BoundKind::Get`.
- Updating `BoundKind::DefLocal` and `BoundKind::Set` to maintain the
  substitution map for local variables.
- Adjusting `try_beta_reduce` to use the optimizer's `visit_node` with
  the substitution map for inlining.
- Re-indexing upvalues correctly when inlining captured variables into
  lambdas.

src/ast/compiler/tco.rs

@@ -3,7 +3,9 @@ use crate::ast::nodes::Node;
 use crate::ast::compiler::bound_nodes::{BoundKind, TypedNode};
 use crate::ast::types::StaticType;
 
-#[derive(Debug, Clone)]
+use std::fmt::Debug;
+
+#[derive(Clone)]
 pub struct RuntimeMetadata {
     pub ty: StaticType,
     pub is_tail: bool,
@@ -11,6 +13,15 @@ pub struct RuntimeMetadata {
     pub original: Rc<TypedNode>,
 }
 
+impl Debug for RuntimeMetadata {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Metadata")
+            .field("ty", &self.ty)
+            .field("is_tail", &self.is_tail)
+            .finish()
+    }
+}
+
 /// The ExecNode is the AST used by the VM. It carries TCO flags and links to source.
 pub type ExecNode = Node<BoundKind<RuntimeMetadata>, RuntimeMetadata>;