Rsync for Windows Native Port

I was always annoyed at needing MSYS2 or Cygwin to get rsync on Windows, so I pointed Claude at it and let it rip. Full session log is in WINDOWS-PORT.md in the repo, and it works in server mode via the Windows OpenSSH Server as well, there's a helper script to set that up. Original sources barely touched, much is added to new translation units that are then selectively compiled in. Some features are disabled, permissions / ACLs, hardlinks, and symlinks; you're not going to want to run in archive mode, stick to -rtv --progress and it works fine.