Only allow @types packages in devDependencies

Only allow TypeScript @types packages from being used anywhere other than in the devDependencies section of package.json.

1. Add a version group

• Match all dependencies whose name starts with @types/.
• Only match those dependencies when they appear anywhere except devDependencies.
• Define the behaviour of this group as isBanned.
• Add a label to document the decision/expectation.

.syncpackrc

{
  "versionGroups": [
    {
      "dependencies": ["@types/**"],
      "dependencyTypes": ["!dev"],
      "isBanned": true,
      "label": "@types packages should only be under devDependencies"
    }
  ]
}

2. Look for mismatches

Any @types packages which are in the wrong location can then be found and manually moved:

syncpack list-mismatches