Resolve smoltcp#1010

[MabezDev]

If we don't resolve smoltcp-rs/smoltcp#1010 we will have a lot of smoltcp features until it's 1.0 release.

[bjoernQ]

In the meantime we could also remove the smoltcp dependency and have a new crate implementing the smoltcp device for different versions of smoltcp - the problem is the same but then it's moved to another crate. We can also keep that crate for when there is a dedicated driver crate - and also it will take time until the whole ecosystem is using the driver crate (e.g. smoltcp-nal is still on smoltcp 0.11)

Update: We can also move the embassy-net-driver impl there if we decide to do sth like that at all

[bugadani]

smoltcp-rs/smoltcp#1080 opened for feedback, pending that we may or may not want to create adapter crates.

[bjoernQ]

Another option would be to remove smoltcp completely and make sure that implementing Device on the user side is as easy as copying a couple of lines from the docs - would also fit the "strategy" to push users to async (by removing the blocking examples from the repo)

Edit: We could even provide a macro to create a smoltcp Device - or have that in a separate crate