chore(deps): update dependency tsdown to ^0.21.1

Author: renovate[bot]

package.json

@@ -35,7 +35,7 @@
     "eslint": "^9.39.2",
     "jsdom": "^27.3.0",
     "prettier": "3.7.3",
-    "tsdown": "^0.17.0-beta.5",
+    "tsdown": "^0.21.1",
     "tslib": "^2.8.1",
     "typescript": "~5.9.3",
     "vite": "^7.2.6",