Declare tsx as a root devDependency so the map/filter differential runs in CI

The map-filter-native differential spawns `pnpm exec tsx` for its on/off child
process. tsx was only a devDependency of the examples workspace, so it resolved
locally through hoisting but was absent from a clean --frozen-lockfile install,
failing pnpm test in CI. Test-infra only; the published packages are unaffected.

Author: MesTTo

package.json

@@ -32,6 +32,7 @@
     "mitata": "^1.0.34",
     "prettier": "^3.8.4",
     "tsup": "^8.3.5",
+    "tsx": "^4.22.4",
     "typescript": "^5.6.3",
     "typescript-eslint": "^8.62.0",
     "vitest": "^2.1.8"