fix random item draw (dragoon/komodo!127)

related to
- !122

## description
!122 introduced a `draw_unique_indices` function which uses a `HashSet` to accumulate unique indices in the range `0..<len`.
however, a `HashSet` does not preserve the order of insertion when iterating over the elements of the set... which results in apparent randomness, even though the RNG seed is the same 😮 

this MR switches back to using `shuffle` which used to work, even though a bit less performant 👌   
it's basically a revert of !122, while keeping the refactoring into `random.rs`.

## measuring the performance
i did run the same timing experiment from !122 but with `main` on `bb55005f` and the MR on `fix-shuffle`

| env     | main                   | mr                      | improvement         |
| ------- | ---------------------- | ----------------------- | ------------------- |
| fixed:0 | 6sec 244ms 238µs 45ns | 8sec 734ms 929µs 328ns | -39.88783363238997  |
| fixed:1 | 639ms 720µs 39ns      | 731ms 360µs 261ns      | -14.325051024390373 |

we loose a bit