bug: Remove `todo!` in deletion vector code. Replace it with an error

[OussamaSaoudi]

We have an instance of todo!() in production code, which may cause a panic. However, kernel should avoid panicking. See the following locations in the code an make it return an error instead.:

kernel/src/actions/deletion_vector.rs
167:                        todo!("Don't support native serialization in inline bitmaps yet");

[Auxilus08]

Hi @OussamaSaoudi, I'd like to work on this issue. I've already prepared a fix that replaces the todo!() macro with a proper error return in kernel/src/actions/deletion_vector.rs at line 167.

The fix converts:

todo!("Don't support native serialization in inline bitmaps yet");