Remove unused imports in parser.rs

Box return values in LoxError

- Box Return.value in LoxError
- Deref boxed value when assigning to ret
- Box value when constructing Return variants
- Update Cargo.toml edition to 2024 and add nightly toolchain

src/common/lox_result.rs

@@ -28,7 +28,7 @@ pub enum LoxError {
     },
     Return {
         source_slice: SourceSlice,
-        value: BaseValue,
+        value: Box<BaseValue>,
         return_label: String,
     },
 }