style: Apply Prettier formatting with 4-space indentation

Applied consistent code formatting across the project using Prettier, now configured to use 4-space indentation instead of tabs.

src/index.test.ts

@@ -1,7 +1,7 @@
 import { describe, it, expect } from 'vitest';
 
 describe('sum test', () => {
-	it('adds 1 + 2 to equal 3', () => {
-		expect(1 + 2).toBe(3);
-	});
+    it('adds 1 + 2 to equal 3', () => {
+        expect(1 + 2).toBe(3);
+    });
 });