rp2040 Interpolator Support

[orukusaki]

In my project I'm making heavy use of the rp2040's interpolators, which are currently unsupported in embassy_rp. When moving from rp2040_hal to embassy_rp, I reimplemented support by taking the code from rp2040_hal::sio and modifying it to work with rp_pac as its base, rather than rp2040_pac, but keeping the interface the same. I'm happy to tidy it up and submit as a PR if:

1. Anyone is interested in having interpolator support in embassy_rp
2. People feel this is the right approach, rather than creating a different implementation from scratch.