Hostless tests no longer crash inside workspace schemes

tuist test on autogenerated workspace schemes no longer crashes when the workspace mixes an app-hosted test bundle with a host-less unit test bundle. When the workspace scheme contains host-less unit tests, tuist test now runs the generated project schemes that cover the scheme’s test targets separately, with --test-targets and --skip-test-targets filtered per split scheme. Running tests through an explicit --scheme flag is unchanged.