chore: tighten lint rules and tests

vitest.config.ts

@@ -11,10 +11,10 @@ export default defineConfig({
       include: ['src/**/*.ts'],
       exclude: ['src/index.ts'],
       thresholds: {
-        statements: 70,
-        branches: 70,
-        functions: 70,
-        lines: 70,
+        statements: 90,
+        branches: 80,
+        functions: 90,
+        lines: 90,
       },
     },
   },