feat: use embedded_hal_async & remove async features

[elpiel]

A few outstanding issues:

• Even if we add a feature to enable async that could complicate the code for the crate as we not only need to deasync all traits, methods and but also remove the .await points with cfg or cfg_if which I'm not sure if it's possible and how well will play with the API and maintainability
• Even though I will try to test the crate on an embedded system, I would like to see an example of how to setup an SD card and some docs surrounding it, as it's not clear to me how to set it up, as I'm not that familiar with the SD card standard and protocol

Until there is a common word like the proposed ?async (I believe it was called) which marks methods as usable as either async or not the best course of action which I've seen crate API implement is duplicating the interface with async.

[qiuchengxuan]

• I've using deasync in multiple crates and it works fine
• Perhaps you would take a look at sdmmc-test.