Refactor Destructure to handle assignments

Renames `DefDestructure` to `Destructure` to better reflect its use in
both definitions and assignments.
Introduces `bind_assign_pattern` to handle assignment destructuring in
the binder.
Adds `test_assign_destructuring` to verify assignment destructuring
functionality.

src/ast/compiler/tco.rs

@@ -118,7 +118,7 @@ impl TCO {
                 global_index: *global_index,
                 value: Box::new(Self::transform(Rc::new((**value).clone()), false)),
             },
-            BoundKind::DefDestructure { pattern, value } => BoundKind::DefDestructure {
+            BoundKind::Destructure { pattern, value } => BoundKind::Destructure {
                 pattern: Box::new(Self::transform(Rc::new((**pattern).clone()), false)),
                 value: Box::new(Self::transform(Rc::new((**value).clone()), false)),
             },