feat: Implement AST binder and VM

Adds a new `Binder` struct that traverses the AST and resolves variable
references to concrete `Address` types (Local, Upvalue, Global). This
information is crucial for the Virtual Machine's execution phase.

Introduces the `BoundKind` enum to represent the AST after binding.

The `VM` is updated to handle `BoundKind` nodes and execute the bound
AST.
It now manages a call stack, local variables, and closures for function
calls and upvalue capturing.

The `Environment` struct is enhanced to manage global variables and
provide
a unified interface for parsing, binding, and executing scripts. It also
includes basic standard library functions.

src/ast/compiler/bound_nodes.rs

@@ -0,0 +1,56 @@
+use std::sync::Arc;
+use crate::ast::types::Value;
+use crate::ast::nodes::{Node, CustomNode};
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Address {
+    Local(u32),   // Stack-Slot index (relative to frame base)
+    Upvalue(u32), // Index in the closure's upvalue array
+    Global(u32),  // Index in the global environment vector
+}
+
+#[derive(Debug)]
+pub enum BoundKind {
+    Nop,
+    Constant(Value),
+    
+    // Variable Access (Resolved)
+    Get(Address),
+    
+    // Variable Update (Resolved)
+    Set {
+        addr: Address,
+        value: Box<Node<BoundKind>>,
+    },
+
+    If {
+        cond: Box<Node<BoundKind>>,
+        then_br: Box<Node<BoundKind>>,
+        else_br: Option<Box<Node<BoundKind>>>,
+    },
+    
+    // Global Definition (Locals are implicit by stack position)
+    DefGlobal {
+        global_index: u32,
+        value: Box<Node<BoundKind>>,
+    },
+
+    Lambda {
+        param_count: u32,
+        // The list of variables captured from enclosing scopes
+        upvalues: Vec<Address>, 
+        body: Arc<Node<BoundKind>>,
+    },
+
+    Call {
+        callee: Box<Node<BoundKind>>,
+        args: Vec<Node<BoundKind>>,
+    },
+
+    Block {
+        exprs: Vec<Node<BoundKind>>,
+    },
+
+    // Extension points (need to be adapted for bound nodes if they use variables)
+    // For now, we assume extensions are self-contained or handled dynamically.
+}