Add ArrayElement type helper

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@extollo/lib",
-  "version": "0.9.48",
+  "version": "0.9.49",
   "description": "The framework library that lifts up your code.",
   "main": "lib/index.js",
   "types": "lib/index.d.ts",

src/util/support/types.ts

@@ -80,3 +80,6 @@ export type Integer = TypeTag<'@extollo/lib.Integer'> & number
 export function isInteger(num: number): num is Integer {
     return !isNaN(num) && parseInt(String(num), 10) === num
 }
+
+export type ArrayElement<ArrayType extends readonly unknown[]> =
+    ArrayType extends readonly (infer ElementType)[] ? ElementType : never;