Mio 1.8.8 incompatible with newer Tokio versions

[Snowda]

Versions of Tokio >=1.34 and higher require Mio >=1.8.9 and causes a version conflict when compiling as coap uses 1.8.8.

A semver bump may resolve this unless there are other aspects that this introduces that would need testing first?

[Covertness]

I think it's no big deal because the difference in version numbers is not very big. You can have a try.

[osobiehl]

I think we can even just remove mio as a dependency now. we do not use it directly

[Covertness]

Yeah. It was added because mio had a issue on Windows. Now the problem had been fixed.