Fix asynchronous appEntrypoint support

[michaelhthomas]

Changes

Fixes #9557, a regression which has broken the (admittedly niche) use case of an asynchronous appEntrypoint function. The changes introduced in #9362 led the potentially asynchronous setup method to be wrapped in a synchronous function, making the await setup() in [server,client].js more-or-less useless. This PR makes the virtual module's wrapper method async as well, bringing back support for asynchronous appEntrypoints.

Testing

A simple test for this scenario was added, which leverages two components registered globally in the appEntrypoint script separated by a simulated asynchronous call to ensure that registration works correctly following an async call within an async entrypoint script.

Docs

Not sure if docs will be needed as this is a pretty niche use case, but it is certainly nice to have. I'll be happy to add to the docs if it would be appropriate.
/cc @withastro/maintainers-docs

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[bluwy]

Thanks for the fix! The PR that regresses this certainly looked unintended, so I made this a patch fix instead. I don't think we need a specific documentation for this too. Sync/Async should work ootb without documenting.