build: downgrade undici to v6

resolves #135

Author: pi0

package.json

@@ -131,8 +131,8 @@
     "proxy-agent": "^6.5.0",
     "typescript": "^5.7.3",
     "unbuild": "^3.3.1",
-    "undici": "^7.2.3",
+    "undici": "^6.21.1",
     "vitest": "^3.0.2"
   },
   "packageManager": "pnpm@9.15.4"
-}
+}