vite-plugin-mud should resolve worldsFile as import path

I would expect something like this to work
```ts
export default defineConfig({
  plugins: [react(), mud({ worldsFile: "@dust/world/worlds.json" })],
```

Current workaround is
```ts
export default defineConfig({
  plugins: [react(), mud({ worldsFile: "node_modules/@dust/world/worlds.json" })],
```

We could probably lift out the logic from CLI that handles both import and relative paths