fix feature dependencies and imports (!164)

in !162 and !163, i did only run `cargo ... --all-features` without checking the individual features...

this MR adds some `cargo check --features ...` to the `Makefile` and makes sure the imports make sense when compiling a single feature.

>  **Important**
>
> the other notable change here is that `kzg::commit` has been moved to `zk::ark_commit` and is re-exported from `kzg` as `kzg::commit`.