We should `impl AsRef<[u16]> for Plane` depending on the bit_depth

[haixuanTao]

Currently, we only retrieve raw parts of Plane as u8 independently from the data being coded with a 10 or 12 bit depth and I think it would be convenient to reference a plane as a u16 when it is the appropriate type.

Thanks for this awesome crate :)

[sdroege]

I'm using https://docs.rs/byte-slice-cast for that purpose, FWIW.

[haixuanTao]

Yeah, I use https://docs.rs/bytemuck/latest/bytemuck/ same thing :)