Re-export pep440 & pep508 types

I was integrating rip into rattler-build (to generate recipes) and had to figure out the right version of pep508 to use. I think it would be better if we re-export it so that users can easily use these types through rip and get the right version.

I think that is a very good idea, especially since we use these types pretty integrally throughout the code. Reexporting the types from those crates makes a lot of sense to me.