Remove passing IO#copy_stream tags.
More disentangling File from ChannelDescriptor, plus umask fix.
Start using native IO for files when possible.
Re-port IO.binwrite/write logic
Fixes to get copy_stream working with native channels.
Rewrite select logic to match MRI. IO and File CI specs 100%.
Remove more passing IO/File tags.
More specs to untag and some thread logic for flock.