chore(deps-dev): Bump tsdown from 0.20.3 to 0.21.0 (#254)

Bumps [tsdown](https://github.com/rolldown/tsdown) from 0.20.3 to 0.21.0.
- [Release notes](https://github.com/rolldown/tsdown/releases)
- [Commits](rolldown/tsdown@v0.20.3...v0.21.0)

---
updated-dependencies:
- dependency-name: tsdown
  dependency-version: 0.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package.json

@@ -25,7 +25,7 @@
     "make-fetch-happen": "^15.0.3",
     "npm-run-all": "^4.1.5",
     "prettier": "^3.7.4",
-    "tsdown": "^0.20.1",
+    "tsdown": "^0.21.0",
     "typescript": "^5.3.3",
     "typescript-eslint": "^8.56.0",
     "vitest": "^4.0.15"