chore(test): load Vitest config as ESM

vitest.config.mts

@@ -0,0 +1,17 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    environment: "node",
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "json-summary"],
+      include: ["lib/**/*.ts"],
+    },
+  },
+  resolve: {
+    alias: {
+      "@": new URL("./", import.meta.url).pathname,
+    },
+  },
+});