Update testing framework to Vitest (#4)

vitest.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    environment: "node",
+    include: ["src/**/*.test.ts"],
+    exclude: ["dist/**", "node_modules/**"],
+    sequence: { hooks: "list" },
+    globals: false,
+    testTimeout: process.env.SMOKE === "1" ? 30000 : 5000,
+    coverage: {
+      provider: "v8",
+      reportsDirectory: "coverage",
+      reporter: ["text", "lcov"],
+    },
+  },
+});