fix: polyfill buffer, shim randombytes

[phanshiyu]

What

1. remove direct use of crypto and instead use https://www.npmjs.com/package/randombytes, which uses native crypto methods based on environment
2. use https://www.npmjs.com/package/buffer instead of relying on buffer from node env

Tested

1. CRA - works out of the box
2. React vite needs

// vite.config.ts
export default defineConfig({
  plugins: [react()],
  define: {
    // By default, Vite doesn't include shims for NodeJS/
    // necessary for segment analytics lib to work
    global: 'globalThis'
  },  
})

3. next server side - out of the box
4. next client side - have to install undici

[github-actions]

🎉 This PR is included in version 6.10.0-alpha.5 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

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