Refactor bound node types for clarity

Introduce generic `CompilerPhase` trait to unify different stages of the
bound AST. Rename `LocalSlot` to `VirtualId` and introduce `StackOffset`
for clearer distinction between compile-time and run-time addressing.
Update type aliases and implementations to reflect these changes.

src/ast/compiler/binder.rs

@@ -1,5 +1,5 @@
 use crate::ast::compiler::bound_nodes::{
-    Address, BoundKind, DeclarationKind, GlobalIdx, LocalSlot, Node, UpvalueIdx,
+    Address, BoundKind, BoundPhase, DeclarationKind, GlobalIdx, Node, UpvalueIdx, VirtualId,
 };
 use crate::ast::diagnostics::Diagnostics;
 use crate::ast::nodes::{Symbol, SyntaxKind, SyntaxNode};
@@ -9,7 +9,7 @@ use std::rc::Rc;
 
 #[derive(Debug, Clone)]
 pub struct LocalInfo {
-    pub addr: Address,
+    pub addr: Address<VirtualId>,
     pub identity: Identity,
     pub _ty: StaticType,
     pub purity: Purity,
@@ -38,7 +38,7 @@ struct FunctionCompiler {
     identity: Identity,
     scopes: Vec<CompilerScope>,
     slot_count: u32,
-    upvalues: Vec<Address>,
+    upvalues: Vec<Address<VirtualId>>,
 }
 
 impl FunctionCompiler {
@@ -65,7 +65,7 @@ impl FunctionCompiler {
         }
     }
 
-    fn define_variable(&mut self, name: &Symbol, identity: Identity) -> Result<Address, String> {
+    fn define_variable(&mut self, name: &Symbol, identity: Identity) -> Result<Address<VirtualId>, String> {
         let current_scope = self.scopes.last_mut().unwrap();
         if current_scope.locals.contains_key(name) {
             return Err(format!(
@@ -74,7 +74,7 @@ impl FunctionCompiler {
             ));
         }
 
-        let slot = LocalSlot(self.slot_count);
+        let slot = VirtualId(self.slot_count);
         current_scope.locals.insert(
             name.clone(),
             LocalInfo {
@@ -97,7 +97,7 @@ impl FunctionCompiler {
         None
     }
 
-    fn add_upvalue(&mut self, addr: Address) -> UpvalueIdx {
+    fn add_upvalue(&mut self, addr: Address<VirtualId>) -> UpvalueIdx {
         if let Some(idx) = self.upvalues.iter().position(|&a| a == addr) {
             return UpvalueIdx(idx as u32);
         }
@@ -114,7 +114,7 @@ pub enum ExprContext {
 }
 
 pub type BindingResult = (
-    Node,
+    Node<BoundPhase>,
     HashMap<Identity, Vec<Identity>>,
     Vec<CompilerScope>,
     u32,
@@ -179,7 +179,7 @@ impl Binder {
         identity: Identity,
         _kind: crate::ast::compiler::bound_nodes::DeclarationKind,
         diag: &mut Diagnostics,
-    ) -> Option<Address> {
+    ) -> Option<Address<VirtualId>> {
         let current_fn_idx = self.functions.len() - 1;
 
         if current_fn_idx == 0 {
@@ -211,7 +211,7 @@ impl Binder {
         node: &SyntaxNode,
         ctx: ExprContext,
         diag: &mut Diagnostics,
-    ) -> Node {
+    ) -> Node<BoundPhase> {
         match &node.kind {
             SyntaxKind::Nop => self.make_node(node.identity.clone(), BoundKind::Nop),
             SyntaxKind::Constant(v) => {
@@ -361,7 +361,7 @@ impl Binder {
                 let body_bound = self.bind(body.as_ref(), ExprContext::Expression, diag);
                 let compiled_fn = self.functions.pop().unwrap();
 
-                fn count_params(node: &Node) -> Option<u32> {
+                fn count_params(node: &Node<BoundPhase>) -> Option<u32> {
                     match &node.kind {
                         BoundKind::Define {
                             kind: DeclarationKind::Parameter,
@@ -520,9 +520,9 @@ impl Binder {
                 );
                 self.make_node(node.identity.clone(), BoundKind::Error)
             }
-            SyntaxKind::Error => crate::ast::compiler::bound_nodes::Node {
+            SyntaxKind::Error => Node {
                 identity: node.identity.clone(),
-                kind: crate::ast::compiler::bound_nodes::BoundKind::Error,
+                kind: BoundKind::Error,
                 ty: (),
             },
         }
@@ -533,7 +533,7 @@ impl Binder {
         sym: &Symbol,
         diag: &mut Diagnostics,
         identity: &Identity,
-    ) -> Option<Address> {
+    ) -> Option<Address<VirtualId>> {
         let current_fn_idx = self.functions.len() - 1;
 
         // 1. Try local in current function
@@ -603,7 +603,7 @@ impl Binder {
         node: &SyntaxNode,
         kind: DeclarationKind,
         diag: &mut Diagnostics,
-    ) -> Node {
+    ) -> Node<BoundPhase> {
         match &node.kind {
             SyntaxKind::Identifier(sym) => {
                 if let Some(addr) = self.declare_variable(sym, node.identity.clone(), kind, diag) {
@@ -647,7 +647,7 @@ impl Binder {
         &mut self,
         node: &SyntaxNode,
         diag: &mut Diagnostics,
-    ) -> Node {
+    ) -> Node<BoundPhase> {
         match &node.kind {
             SyntaxKind::Identifier(sym) => {
                 if let Some(addr) = self.resolve_variable(sym, diag, &node.identity) {
@@ -684,7 +684,7 @@ impl Binder {
         }
     }
 
-    fn make_node(&self, identity: Identity, kind: BoundKind<()>) -> Node {
+    fn make_node(&self, identity: Identity, kind: BoundKind<BoundPhase>) -> Node<BoundPhase> {
         Node {
             identity,
             kind,