Suite shard planning recovers or fails loud on flaky test enumeration

Suite-granularity shard planning no longer silently drops test targets whose bundle fails to bootstrap under simulator boot contention. Such targets are now re-enumerated in isolation (which recovers the missing suites reliably), top-level @Test Swift Testing functions are now counted as tests, and the underlying xcodebuild errors are surfaced so the planner fails loudly with modulesFailedToEnumerate instead of shipping a short plan when recovery fails.