Refactor NodeIdentity to use unique IDs

The `NodeIdentity` struct has been refactored to use a unique `id` field
generated by an atomic counter. This ensures that each `NodeIdentity`
instance is distinct, even if it has the same `SourceLocation`. The
`location` field is now optional, allowing for anonymous nodes.

This change improves the reliability of identity comparisons and
provides a more robust way to manage AST node identities.

src/ast/compiler/binder.rs

@@ -130,9 +130,7 @@ impl Binder {
         };
         binder.functions.push(FunctionCompiler::new(
             ScopeKind::Root,
-            Rc::new(crate::ast::types::NodeIdentity {
-                location: crate::ast::types::SourceLocation { line: 0, col: 0 },
-            }),
+            crate::ast::types::NodeIdentity::new(crate::ast::types::SourceLocation { line: 0, col: 0 }),
         ));
         binder
     }