Host-less tests isolated in workspace test runs

Default tuist test runs no longer crash with xctest at <external symbol> when the autogenerated workspace scheme mixes app-hosted and host-less unit test bundles. When host-less tests are present, the run is split into per-project schemes and --test-targets/--skip-test-targets are filtered per split, so a request for FeatureTests no longer accidentally runs AppTests. Explicit tuist test --scheme ... behavior is unchanged.