Reliable upload of large selective-testing bundles

Tuist can now upload very large selective-testing bundles (hundreds of modules, multi-GB) without running out of memory. The multipart upload now keeps at most 10 parts in flight at once, so peak memory per upload is bounded instead of scaling with the artifact size. Per-module .xctest archives are also written in place from the products directory via Apple Archive, avoiding the previous copy-into-staging step that cost tens of GB of redundant disk I/O on big build jobs. Smaller selective-testing bundles continue to work as before.