Changes
### Added
- Closures accept a return type: `function () -> int { }`, in all eight closure forms (with or without a parameter list, with or without a `use (...)` clause, with or without a body). The type follows the `use (...)` clause, mirroring PHP's `function () use ($x): int`, and reuses the method return-type grammar, so `void`, unions (`int|string`) and `` casts are accepted. The closure node gains a `return-type` key, emitted only when a type is present ([zephir-lang/zephir#1841](https://github.com/zephir-lang/zephir/issues/1841)).