Add sync prop to <CodeGroup> to disable cross-instance tab synchronization

[viveralia]

Problem

When a page has multiple <CodeGroup> instances with matching tab labels, switching a tab in one group automatically switches all others on the page. If the code blocks across groups have different content heights, this causes noticeable layout shifts — the page jumps as multiple containers resize simultaneously, often scrolling the user away from what they were reading.

Where to reproduce

Fingerprint Docs

This page has several <CodeGroup> instances with tabs like "NPM", "CDN", etc. Switching tabs in any one of them causes all others to switch too, producing a jarring scroll jump.

Expected behavior

The <Tabs> component already supports a sync={false} prop to disable cross-instance synchronization. The same prop should be available on <CodeGroup>, allowing authors to opt out of sync behavior on pages where the layout shift is disruptive.

<CodeGroup sync={false}>
  ```js NPM
  // ...
// ...

Why this matters

Migration guides and comparison pages naturally have many code groups showing before/after or step-by-step changes. These groups often have very different content sizes per tab, making the synchronized resizing especially disruptive. Being able to disable sync per <CodeGroup> would keep the default behavior everywhere it works well while giving authors control on pages where it doesn't.