Option::as_slice and as_mut_slice

[danakj]

https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_slice

Stabilized in 1.75.0 and can be added to sus::Option, working with Slice and SliceMut.

[Ananyasingh2002]

Please assign me this task!

[danakj]

Hey, you can just send a PR to add the functions and tests. :) Thanks!