Re-export mlir_sys

[cospectrum]

To close #583

[raviqqe]

@edg-l Do you think this is a good change?

I feel like this is the responsibility of the package manager (i.e. Cargo.) But at the same time, I've never hit problems @cospectrum described in the original issue.

[edg-l]

I dont have an opinion on this, but with cargo you can have multiple versions with package renaming

[raviqqe]

@edg-l Yeah, that's what I've suggested in #583 too.

@cospectrum How critical is this change to your workflow?

[cospectrum]

Well, that's quite important for me. Every time I run cargo update, for example, the workspace has a chance to not compile anymore, and cargo will not prevent it. To fix the compile error, I should find melior version in Cargo.lock, then find out exact version of its mlir_sys somewhere (crates.io or lock file), and then I should downgrade my own mlir_sys in Cargo.toml manually.