chore: Upgrade to Node 20

Author: wottpal

.nvmrc

@@ -0,0 +1 @@
+v20

package.json

@@ -4,15 +4,18 @@
   "author": "Scio Labs <[email protected]> (https://scio.xyz)",
   "type": "module",
   "version": "1.0.0",
+  "engines": {
+    "node": ">=18 <=20"
+  },
   "scripts": {
     "build": "tsc",
     "node": "substrate-contracts-node --dev --base-path ./.node-data",
     "script": "f() { tsx ./src/$1; }; f \"$@\"",
     "type-check": "tsc --pretty --noEmit"
   },
   "devDependencies": {
-    "@types/node": "^18.18.9",
     "@polkadot/types": "^10.11.1",
+    "@types/node": "^20.10.0",
     "tsx": "^4.5.0",
     "typescript": "^5.3.2"
   },