Workspace test schemes isolate hostless unit test bundles

Default tuist test runs that mix app-hosted and host-less unit test bundles no longer run the autogenerated workspace aggregate, which under Xcode 26 crashes xctest during bootstrap. The selected test scheme, split project schemes per target, or skipped-when-empty schemes are used depending on the workspace’s content, with –test-targets/–skip-test-targets filtered per split scheme so a request for FeatureTests no longer runs AppTests.