feat: implement cdc application layer, fix enumeration

feat: add rx data callback, increase tx fifo size

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.

chore: update pin, exti, delay

docs: add documentation comments to most functions

feat: implement usb devicd cdc descriptors, init, setup

feat: move all sending instructions to generic send functions

feat: implement most of enumeration

feat: receive setup packets

wip: usb

feat: add registers, pin, exti, usb_device skeleton