Reliable suite-granularity shard planning from server history

Sharded test runs now plan suite-level shards from server-side historical test data instead of having the CLI boot every test bundle’s runner, which could fail under simulator boot contention with errors like “Early unexpected exit, operation never finished bootstrapping”. The CLI reads test modules from the built .xctestrun, the server derives per-module suite inventory from the latest CI run on the branch (with a default-branch fallback), the final shard acts as a catch-all skip-testing shard so newly added suites are never dropped, and module-level sharding is unchanged. Older CLIs continue to receive legacy shard shapes.