add msc support for embassy-usb, tested on stm32g431cbu6

[fan2nd]

No description provided.

[felipebalbi]

If you have access to a windows machine, it's a good idea to run this against the USB Command Verifier tool and make sure you connect this to as many different hosts as you can grab. MSC is one of the classes with the quirkiest implementations out there. Of course, it's unlikely to be a blocker to this PR, but if you can find potential quirks early on, might as well.

[fan2nd]

If you have access to a windows machine, it's a good idea to run this against the USB Command Verifier tool and make sure you connect this to as many different hosts as you can grab. MSC is one of the classes with the quirkiest implementations out there. Of course, it's unlikely to be a blocker to this PR, but if you can find potential quirks early on, might as well.

Thanks for your suggestion, I'll give it a try.

[elipsitz]

In #2837, someone pointed limitations with the current USB API (inability to stall an endpoint?) that prevent MSC from being properly implemented. I'm not actually very familiar with the spec, but do you know if those limitations cause any problems here?