fix(clerk-js): Correct race condition when fetching tokens

[jacekradko]

Description

Fix race condition where multiple browser tabs could fetch session tokens simultaneously. The refreshTokenOnFocus handler now uses the same cross-tab lock as the session token poller, preventing duplicate API calls when switching between tabs or when focus events fire while another tab is already refreshing the token.

Checklist

• [ ] pnpm test runs as expected.
• [ ] pnpm build runs as expected.
• [ ] (If applicable) JSDoc comments have been added or updated for any package exports
• [ ] (If applicable) Documentation has been updated

Type of change

• [ ] 🐛 Bug fix
• [ ] 🌟 New feature
• [ ] 🔨 Breaking change
• [ ] 📖 Refactoring / dependency upgrade / documentation
• [ ] other:

Summary by CodeRabbit

• Bug Fixes

  • Fixed race conditions that could cause duplicate session token fetches across tabs, reducing unnecessary network calls and sign-in glitches.
  • Improved session polling reliability so retries are rescheduled even after errors.

• New Features

  • Added a cross-tab locking utility to coordinate token fetches and avoid redundant requests.
  • Added ability to stop and restart session polling.

• Tests

  • Added comprehensive tests for polling, locking, and token refresh sequencing.

• Chores

  • Added a changeset for a patch release.

_{✏️ Tip: You can customize this high-level summary in your review settings.}