fix: update types isInstance

Author: bigmistqke

src/utils/is-instance.ts

@@ -1,5 +1,5 @@
 import type { Instance } from "src/types.ts"
 import { $S3C } from "../constants.ts"
 
-export const isInstance = <T extends object>(element: T): element is Instance<T> =>
-  typeof element === "object" && $S3C in element
+export const isInstance = <T>(element: T): element is Instance<T> =>
+  typeof element === "object" && element && $S3C in element