fix(types): make JsonifiableObject extendable

Signed-off-by: Lexus Drumgold <[email protected]>

src/types/jsonifiable-object.ts

@@ -6,12 +6,15 @@
 import type Jsonifiable from './jsonifiable'
 
 /**
- * Matches an object whose items can be losslessly converted to JSON.
+ * Matches an object that can be losslessly converted to JSON.
  *
- * @see [`Jsonifiable`]({@link ./jsonifiable.ts})
+ * For objects with `toJSON` methods, use [`JsonifiableInstance`][1] instead.
+ *
+ * [1]: {@link ./jsonifiable-instance.ts}
+ * [2]: {@link ./jsonifiable.ts}
+ *
+ * @see [`Jsonifiable`][2]
  */
-type JsonifiableObject =
-  | { [K in string]?: Jsonifiable }
-  | { toJSON(): Jsonifiable }
+type JsonifiableObject = { [K in string]?: Jsonifiable }
 
 export type { JsonifiableObject as default }