Add a test which verifies that Blackholio's types generated from Rust can be used with the C# module and vice versa

DOD: We have a test in the blackholio repo which verifies that you can use the Rust module to generate types for use in Unity, and then you can connect to the C# module (and vice versa).

You can't:

spacetime generate --lang csharp -p server-rust --out-dir ../client-unity/Assets/autogen
spacetime publish -p server-csharp blackholio
# you get errors when you connect in unity

Nor can you do:

spacetime generate --lang csharp -p server-csharp --out-dir ../client-unity/Assets/autogen
spacetime publish -p server-rust blackholio
# you get errors when you connect in unity

What we should perhaps actually test is that the ModuleDefs are identical.

Start by inspecting the blackholio repository's existing test setup and the spacetime generate and spacetime publish entry points shown in the issue. Reproduce both Rust/C# generation and publishing directions, then decide whether the test should compare ModuleDefs or verify the Unity connection; done means the cross-language compatibility case is covered.