refactor: replace uuid dep with Node.js built-in crypto.randomUUID (#4377)

Replace the third-party `uuid` package with the native `crypto.randomUUID()`
function available in Node.js, reducing the bundle size and external
dependencies.

- Remove `uuid` from `dependencies` in `package.json`
- Replace `import {v4 as uuidv4} from 'uuid'` with `import {randomUUID} from 'crypto'` in `src/create-or-update-branch.ts`
- Replace all `uuidv4()` calls with `randomUUID()` in `__test__/create-or-update-branch.int.test.ts`
- Rebuild `dist/index.js`, removing ~680 lines of bundled `uuid` library code
- Update `package-lock.json` to reflect removed dependency

Author: peter-evans