Add sideEffects: false for old bundlers to know they can tree-shake the CJS

Vite is smart enough to use the ESM build of these packages, but old bundlers like webpack 4 that aren't need a special indicator that files don't have side effects so they can be tree-shaken away.

This doesn't change the bundle size with vite, but now webpack should be equivalent.

Before:

```
vite v4.4.7 building for production...
✓ 223 modules transformed.
dist/api-read-stats.html      230.59 kB │ gzip: 48.89 kB
dist/test-bundle-api-read.js  253.91 kB │ gzip: 47.33 kB
dist/api-read-stats.html       231.12 kB │ gzip: 48.95 kB
dist/test-bundle-api-read.cjs  168.40 kB │ gzip: 39.39 kB
✓ built in 965ms
vite v4.4.7 building for production...
✓ 499 modules transformed.
dist/react-read-stats.html      321.86 kB │ gzip: 59.00 kB
dist/test-bundle-react-read.js  359.09 kB │ gzip: 76.48 kB
dist/react-read-stats.html       324.49 kB │ gzip: 59.05 kB
dist/test-bundle-react-read.cjs  243.18 kB │ gzip: 64.60 kB
✓ built in 1.34s
vite v4.4.7 building for production...
✓ 1033 modules transformed.
dist/shopify-read-stats.html      534.09 kB │ gzip:  79.63 kB
dist/test-bundle-shopify-read.js  678.46 kB │ gzip: 135.16 kB
dist/shopify-read-stats.html       534.63 kB │ gzip:  79.70 kB
dist/test-bundle-shopify-read.cjs  477.27 kB │ gzip: 115.70 kB
✓ built in 2.50s
```

After:

```
vite v4.4.7 building for production...
✓ 223 modules transformed.
dist/api-read-stats.html      230.59 kB │ gzip: 48.89 kB
dist/test-bundle-api-read.js  253.91 kB │ gzip: 47.33 kB
dist/api-read-stats.html       231.12 kB │ gzip: 48.95 kB
dist/test-bundle-api-read.cjs  168.40 kB │ gzip: 39.39 kB
✓ built in 921ms
vite v4.4.7 building for production...
✓ 499 modules transformed.
dist/react-read-stats.html      321.86 kB │ gzip: 59.00 kB
dist/test-bundle-react-read.js  359.09 kB │ gzip: 76.48 kB
dist/react-read-stats.html       324.49 kB │ gzip: 59.05 kB
dist/test-bundle-react-read.cjs  243.18 kB │ gzip: 64.60 kB
✓ built in 1.27s
vite v4.4.7 building for production...
✓ 1033 modules transformed.
dist/shopify-read-stats.html      534.09 kB │ gzip:  79.63 kB
dist/test-bundle-shopify-read.js  678.46 kB │ gzip: 135.16 kB
dist/shopify-read-stats.html       534.63 kB │ gzip:  79.70 kB
dist/test-bundle-shopify-read.cjs  477.27 kB │ gzip: 115.70 kB
✓ built in 2.45s
```

Author: airhorns

Contributing.md

@@ -16,6 +16,16 @@ It can be annoying to work with these packages via `pnpm link` sometimes, so we
 - push that to the remote git repo
 - and log out a version you can then refer to from other repos
 
+# Checking test bundle sizes
+
+We have a small project setup for evaluating what the bundled size of these dependencies might be together. Run:
+
+```shell
+pnpm -F=test-bundles test-build
+```
+
+to build the test bundles
+
 # Releasing
 
 Releasing is done automatically via [our release workflow](.github/workflows/release.yml). Any commits to the main branch that changes one of our `packages/**/package.json` versions will automatically be published.

packages/api-client-core/package.json

@@ -19,6 +19,7 @@
   },
   "source": "src/index.ts",
   "main": "dist/cjs/index.js",
+  "sideEffects": false,
   "scripts": {
     "typecheck": "tsc --noEmit",
     "build": "rm -rf dist && tsc -b tsconfig.cjs.json tsconfig.esm.json && echo '{\"type\": \"commonjs\"}' > dist/cjs/package.json && echo '{\"type\": \"module\"}' > dist/esm/package.json",

packages/react/package.json

@@ -19,6 +19,7 @@
   },
   "source": "src/index.ts",
   "main": "dist/cjs/index.js",
+  "sideEffects": false,
   "scripts": {
     "typecheck": "tsc --noEmit",
     "build": "rm -rf dist && tsc -b tsconfig.cjs.json tsconfig.esm.json && echo '{\"type\": \"commonjs\"}' > dist/cjs/package.json && echo '{\"type\": \"module\"}' > dist/esm/package.json",