fix feature dependencies and imports

in !162 (merged) and !163 (merged), 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.