Single bitmap implementation for different special cases

[eugene-babichenko]

Now there are two different implementations of bitmaps:

• One in imhamt (32 bits long)
• Another one in sparse-array (256 bits long)

We need to implement a bitmap that will satisfy different corner-cases (8, 16, ... 256 bits) and be reusable so that we can remove functionality duplication.

[mzabaluev]

There may be a performance benefit in keeping at least these two implemented differently, as the first one fits within u32 and the other needs to be backed by an array.

[eugene-babichenko]

Instead we can implement u256 and use something like PrimInt trait from the num crate: struct Bitmap<T: PrimInt>(T).

[NicolasDP]

which reminds me: https://crates.io/crates/uint