Check that extensions are up to date

[Ulthran]

What's the feature?

A common source of bugs with sunbeam extensions is having extensions that aren't up to date with recent GitHub changes. This is the price we pay for trying to walk the line between having a proper version control/matching system for sunbeam with its extensions and just making everything fully backwards/forwards compatible.

Something that might make this problem more palatable is a system to check that all extensions are up to date with GitHub main/master branches (maybe at start of run, maybe a separate command, maybe only on error?).