serial::{Tx, Rx}::{listen, unlisten} are unsafe

[AndreySmirnov81]

And also Rx::{listen_idle, unlisten_idle} are unsafe.

They all use unsafe { (*USART::ptr()).cr1.modify(|_, w| w. ...) };.

It is non-atomic read-modify-write.

Tx and Rx can be used simultaneously from different execution threads.
At the same time, they do not provide thread-safe access.

[burrbull]

technically we could rewrite those with bit-banding (bb::set)

[AndreySmirnov81]

I think this will be the most optimal solution.