hidpp: `RawHidChannel` implementation for `async-hid`

[lus]

async-hid is the crate mostly used during development and testing of the hidpp crate.
Providing a default implementation of RawHidChannel for this crate, possibly behind a feature gate, would help significantly.
To be able to do this, async-hid would need to support exposing raw usage descriptors, which is a feature tracked in sidit77/async-hid#17.