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/macros.rs

@@ -769,7 +769,7 @@ mod tests {
         locals.insert(
             Symbol::from("*"),
             crate::ast::compiler::binder::LocalInfo {
-                addr: Address::Local(crate::ast::compiler::bound_nodes::LocalSlot(0)),
+                addr: Address::Local(crate::ast::compiler::bound_nodes::VirtualId(0)),
                 identity: crate::ast::types::NodeIdentity::new(crate::ast::types::SourceLocation {
                     line: 0,
                     col: 0,