Pass ThreadingContext instead of Pools/Profiler individually, for access to Zones
Add GCPP_ZONE helper
Add Caller argument to pool.Run to enable new stats
Remove most direct dependencies on ThreadPool, prefer ParallelFor
PiperOrigin-RevId: 822934530
(1) Directly write to file in BlobWriter::Add and destruct the MatOwner to release the rams.
(2) Write a fake header to indicate this is V2, and write correct header and directory at the end of the file.
(3) Tested on loading sbs written the old way, and new way, both worked.
PiperOrigin-RevId: 789306837
Jan Wassenberg
Charles Zhao