mbv: i really though async would work this time

There's still a glitch/race somewhere.

mbv/apps/async/uart_async.h

@@ -7,7 +7,7 @@
 #include "buffer.h"
 
 async::task<buffer> UartRead(int size);
-async::task<uint8_t> UartReadLoop();
+async::task<std::byte> UartReadLoop();
 async::task<> UartWrite(std::span<const std::byte> data);
 inline async::task<> UartWrite(std::string_view s) {
     co_await UartWrite(std::as_bytes(std::span{s.data(), s.size()}));