refactor(core/fetch): optimize perfomance, improve types

core/stdlib/src/types/ts/array.ts

@@ -2,3 +2,8 @@
  * A type that can be either a single value or an array of values
  */
 export type Arrayable<T> = T | T[];
+
+/**
+ * A type that can be either a single value or a readonly array of values
+ */
+export type ReadonlyArrayable<T> = T | readonly T[];