chore: hoist text-measure import in yoga.ts; declare node>=22 engine

Addresses PR #23 review: move the mid-file text-measure import to the
top-level import block, and declare engines.node>=22 to match the
upgraded text stack (cli-truncate@6, slice-ansi@9 require node>=22).

packages/runtime/package.json

@@ -46,5 +46,8 @@
   },
   "peerDependencies": {
     "vue": "^3.4.0"
+  },
+  "engines": {
+    "node": ">=22"
   }
 }