Async/Blocking impls

[elpiel]

Let's use a single interface and implement different Modes on the same struct depending on the passed Read instance.

As an example, you can take a look at https://docs.embassy.dev/embassy-rp/git/rp2040/spi/struct.Spi.html
Although the use case is a bit different (implementing the SPI driver at hal level) we can use the exact same approach with Blocking / Async modes and use the same struct with 2 different (or more, see #1 ) implementations.