feat: use task_result to indicate blocking

There should be no spin loops inside of the
interrupts, so this change removes them,
and instead uses a result system that has
WOULD_BLOCK result. When this result is returned,
it is expected there was no side-effect and the
function can safely be reran later.

docs: add documentation comments to most functions

feat: implement usb devicd cdc descriptors, init, setup