Bump tsdown from 0.19.0 to 0.20.3

Bumps [tsdown](https://github.com/rolldown/tsdown) from 0.19.0 to 0.20.3.
- [Release notes](https://github.com/rolldown/tsdown/releases)
- [Commits](rolldown/tsdown@v0.19.0...v0.20.3)

---
updated-dependencies:
- dependency-name: tsdown
  dependency-version: 0.20.3
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

package.json

@@ -48,7 +48,7 @@
     "eslint": "^9.39.1",
     "fastify": "^5.6.2",
     "prettier": "^3.6.2",
-    "tsdown": "^0.19.0",
+    "tsdown": "^0.20.3",
     "typescript": "^5.1.3",
     "vitest": "^4.0.10"
   }