Suite-granularity shard plans no longer silently drop test targets that failed to bootstrap

A suite-granularity shard plan no longer silently drops test targets. XCTestEnumerator now surfaces the errors array from xcodebuild -enumerate-tests so a runner that failed to bootstrap is no longer confused with a genuinely empty target, top-level Swift Testing @Test functions are also captured (not just @Suite classes), and the planner either recovers the missing modules via isolated re-enumeration or throws ShardPlanServiceError.modulesFailedToEnumerate instead of shipping an incomplete plan.