Apple silicon support is missing.

[TWTristan]

Issue Checklist

• I'm using the latest u3d version
• I ran u3d --help
• I read the README
• I made sure that a similar issue doesn't exit

Issue Description

Hello, when I install on Apple silicon it's not downloading and installing the Arm64 build from unity.

In the archive the Arm64 builds are located here:
https://download.unity3d.com/download_unity/eeca29774eb5/MacEditorInstallerArm64/Unity.pkg

While the intel build are located here:
https://download.unity3d.com/download_unity/eeca29774eb5/MacEditorInstaller/Unity.pkg

It would be great if I could at least install it using:
u3d install -p UnityArm64

Would be even better if it just defaulted to this on Apple Silicon.

This is especially important to us because Mac can be used to build both Android and iOS. So we prefer to use macs for our Jenkins agents.