Allow users to specify backend

[abcminiuser]

In my StreamDeck library, users are reporting that the libhid-hidraw0 library fails to write to their devices, while the libhid-libusb0 backend works. Being able to specify which (or any) backend is used would be extremely helpful.

[apmorton]

I will happily review and merge a PR for this and publish any changes to pypi, but unfortunately I don't have much time these days to spend on this project myself.

[robsmith11]

Is there currently any way to specify the backend, even with env variables?