As usual, NuGet / MSBuild behaving differently for local projects vs published ones causes build issues that are not revealed by testing...
This is published to NuGet now and verified to work on an empty project.
Also changed the way `SpacetimeDB.Runtime.{props,targets}` are referenced locally by test projects by moving them to `Directory.Build.{props,targets}` at the top level of `modules/` directory. This should simulate behaviour of published NuGet packages a bit more closely - in particular, I verified that it can reproduce the bug in question before the fix, while the previous `<Import />` approach succeeded regardless - and also makes it easier to share the same configs between multiple projects.
This allows to make and test ABI-breaking changes much more easily than before.
For now moved them under crates/bindings-csharp - on one hand, it's not a crate, but on another it's the most logical place within our current project structure if we think of `crates` folder as general `projects` folder.
Ingvar Stepanyan