Migrate repo from rush to pnpm

[timotheeguerin]

Migrate the repository from rush to pnpm

• Remove all rush files
• Use pnpm to build everything
• Migrate to @chronus/chronus for changelogs.

Example https://github.com/alloy-framework/alloy

[copilot-swe-agent]

@timotheeguerin Unfortunately I hit an unexpected error while trying to work on issue #5114. I've automatically reported this to GitHub.

You can ask me to try again later by unassigning and then reassigning the issue to me again.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: 256b9225-f888-4ec2-9596-f173a68df8b8

Sorry for the inconvenience!