Rust crate publishing (dry-run)

[ngroman]

I think this is a possible fix for #1786

This change consolidates the prism and prism-sys crates into a single workspace that shares one Cargo.lock.

The somewhat unfortunate part here is that for prism-sys I have to use --allow-dirty with cargo publish because the C files and headers that are copied over by rake cargo:build must also be published.

Testing

Ran git clean -xfd && RBENV_VERSION=3.1 bundle exec rake cargo:publish:dry

Note this still fails with error because prism-sys does not exist on crates.io

[kddnewton]

Sorry I didn't manage to get to this this week, I'll work on it next week. At first glance it looks good.

[kddnewton]

@ngroman going to try to publish this today/tomorrow.

[kddnewton]

This is now merged!