test: add initial testing and linting (#18)

vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from 'vitest/config';
+
+const config = defineConfig({
+  test: {
+    coverage: {
+      reporter: ['text', 'json', 'json-summary', 'html'],
+      all: true,
+      reportOnFailure: true,
+      include: ['src/**/*.ts'],
+      exclude: ['src/cli/**/*.ts'],
+    },
+  },
+});
+
+export default config;