Improve project reference in monorepo

[unional]

When using Storybook in monorepo, one way is take the "source project reference" approach:

// apps/app-x/.storybook/main.ts

const config: {
  stories: [
    '../src/**/*.@(mdx|stories.tsx)',
    {
      titlePrefix: 'pkg-a',
      directory: '../../../packages/pkg-a',
      files: 'src/**/*.@(mdx|stories.tsx)'
    }
  ]
}

export default config

With vitest-plugin-vis@3.5.1, we support this case by replacing .. in the path with __.

However, that means the snapshots are created twice: one in the current project and one in the referenced project(s).

Also, this is not ideal when the projects have different settings.

If we can leverage Vitest's projects/workspace feature to run multiple instances and combine the result, that would be ideal.

However, that is not likely the case as we are breaking the project boundary with this "source project reference" approach in Storybook.

Another alternative is to disable or filter to only run snapshots withi3n the current project folder. But that means we will not be able to detect the snapshot failures or show the snaphots of the referenced projects.

A workaround right now is to ignore the snapshots with __/ path in the .gitignore file.

But we should discuss and see what else can be done to improve the system.