chore(deps): update dependency tsdown to ^0.21.0

Author: renovate[bot]

package.json

@@ -13,7 +13,7 @@
     "@types/node": "^22",
     "@typescript/native-preview": "7.0.0-dev.20260109.1",
     "oxlint": "^1.41.0",
-    "tsdown": "^0.20.0",
+    "tsdown": "^0.21.0",
     "typescript": "^5.8.0"
   },
   "version": "0.0.0"