Project Cache: Fix `project:` includes

[bierbaum]

Right now, project includes defined in projects are ignored by the project cache during generation. We should fix this.

   This doesn't allow projects that include sub-project targets, since I wasn't able to continue the work to get the project target resolution into try_from.

If you want all the recursive targets from a project that potentially includes other projects:

let targets = project.resolve_targets_for_project(catalog.optional_projects.underlying)

Originally posted by @conjohnerton in #22 (comment)