Indicate supported version in package.json

Node 16 has been EOL for over a year, and hasn't been tested in CI since #743 was merged last year. The `engines` field in `package.json` should reflect this as well.

package.json

@@ -43,7 +43,7 @@
     }
   },
   "engines": {
-    "node": ">= 10"
+    "node": ">= 18"
   },
   "publishConfig": {
     "registry": "https://registry.npmjs.org/",