feat: do the pick challenge

src/type-challenges/0004-pick/main.ts

@@ -0,0 +1,47 @@
+/**
+ * @copyright NHCarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+
+import type { Equal, Expect } from "@type-challenges/utils";
+
+/**
+ * Original code:.
+ *
+ * ```ts
+ * type MyPick<T, K> = any
+ * ```
+ */
+
+type MyPick<T, K extends keyof T> = {
+  [P in K]: T[P];
+};
+
+/**
+ * Test cases.
+ */
+
+// @ts-expect-error -- Unused variable.
+// eslint-disable-next-line @typescript-eslint/no-unused-vars -- This is necessary for tests.
+type Cases = [
+  Expect<Equal<Expected1, MyPick<Todo, "title">>>,
+  Expect<Equal<Expected2, MyPick<Todo, "title" | "completed">>>,
+  // @ts-expect-error -- Invalid key.
+  MyPick<Todo, "title" | "completed" | "invalid">,
+];
+
+interface Todo {
+  title:       string;
+  description: string;
+  completed:   boolean;
+}
+
+interface Expected1 {
+  title: string;
+}
+
+interface Expected2 {
+  title:     string;
+  completed: boolean;
+}