chore(deps): update dependency tsdown to v0.21.6

Author: renovate[bot]

package.json

@@ -78,7 +78,7 @@
     "react": "19.2.4",
     "react-dom": "19.2.4",
     "rimraf": "6.1.3",
-    "tsdown": "0.21.4",
+    "tsdown": "0.21.6",
     "typescript": "5.9.3",
     "vitest": "4.1.0",
     "vitest-fetch-mock": "0.4.5"