Give cache_exit_snapshot_check's stand-in pipeline state the held sizes cache_save_one now stores.

Since d9429b0c, vk_pipeline.c cache_save_one stores the cache data sizes in P.held for the memory report, and the
check, which builds cache_save_one against a stand-in P, failed to compile ("no member named 'held'"), so the exit
save's snapshot rules went unchecked. The stand-in has the field now; vk_pipeline.c is unchanged.

The check passes again with the ucrt64 clang: builds held back and waited for, autosave unchanged, timeout, failures,
merges and the size limit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/cache_exit_snapshot_check.py

@@ -47,6 +47,7 @@ static struct {
     int device, fold, feedback;
     const char *cache_path, *play_path;
     uint64_t saved[2], cache_loaded, play_loaded;
+    volatile uint64_t held[2];   // cache_save_one stores the data sizes here for the memory report
 } P;
 static void plat_mutex_lock_shared(PlatMutex *m) { AcquireSRWLockShared(m); }
 static void plat_mutex_unlock_shared(PlatMutex *m) { ReleaseSRWLockShared(m); }