Transition to async I/O for most things

Mixing async and sync I/O leads to a multitude of complications, and
generally speaking it's much more convenient to stick to one paradigm
or the other. Since axum (and many other HTTP servers) use async,
and since async is a convenient model for performing operations like
"handle an MPSC message or file read, whichever happens first", let's
commit to an async interface.

lib/src/lib.rs

@@ -1,7 +1,6 @@
 pub mod hdlc;
 pub mod diag;
 pub mod diag_device;
-pub mod diag_reader;
 pub mod qmdl;
 pub mod log_codes;
 pub mod gsmtap;