feat: Add Atlas Stats Output File

[jasongaare]

Summary

Exports a lightweight .expo/atlas-stats.json file when running expo export with Atlas enabled. This file is optimized for CI/CD environments seeking to provide simply bundle size analysis without the full module graph.

Also implements a "stats-only" mode that skips writing the large atlas.jsonl when it isn't needed (i.e. in a CI/CD environment).

Stats file format

  [
    {
      "platform": "ios",
      "environment": "client",
      "entryPoint": "/path/to/app/index.js",
      "bundleSize": 2458624,
      "packages": {
        "react": 85234,
        "react-native": 456789,
        "expo": 123456,
        "@company/ui-lib": 234567
      },
      "files": {
        "app/components/Button.tsx": 2345,
        "app/screens/HomeScreen.tsx": 5678,
        "app/utils/helpers.ts": 1234
      },
      "assets": {
        "assets/images/logo.png": 12345,
        "assets/fonts/custom.ttf": 23456
      }
    }
  ]

Stats-only mode

• Add statsOnly option to withExpoAtlas() config
• Add EXPO_ATLAS_STATS_ONLY environment variable support
• Skip atlas.jsonl creation when stats-only mode is enabled

Usage for stats-only mode

// Via config option                                                     
module.exports = withExpoAtlas(config, { statsOnly: true })              
                                                                         
// Via environment variable                                              
EXPO_ATLAS=1 EXPO_ATLAS_STATS_ONLY=true npx expo export                               

[jasongaare]

@byCedric not sure how much active development is going on with Atlas these days, but I've been using it to write a bundle-change analysis tool for our repo. the output essentially looks like this:

I was having trouble parsing the very large atlas.jsonl file, hence the addition of the simple atlas-stats.json file in this PR.