Move the `Device` trait to `smoltcp-driver`

[MabezDev]

We want to move away from our "home grown" blocking network stack in esp-wifi: https://github.com/esp-rs/esp-hal/pull/2488#issuecomment-2464388663.

The obvious choice is smoltcp-nal, however this often lags behind when it comes to smoltcp release. Due to the fact the Device trait is tied up with the stack, every smoltcp version creates a "unique" and incompatible Device trait, even if the trait didn't change in that release.

embassy-net doesn't suffer from this issue due to the driver trait decoupling, I propose we do the same for smoltp.