feat: add GetArrayItemType to exported types in index.ts

Author: sakobu

src/index.ts

@@ -3,4 +3,4 @@ export * from './useFormAutoSubmission';
 export * from './useDebounce';
 export { fromStandardSchema, isStandardSchema } from './standardSchema';
 export type { FormValidator } from './standardSchema';
-export type { UseFormReturn, ExtractFieldPaths } from './types';
+export type { UseFormReturn, ExtractFieldPaths, GetArrayItemType } from './types';