Update os.copy_file_range documentation #93180

Documentation of os.copy_file_range needs a few updates:

Since Linux kernel 5.3 files pointed by src and dst no longer must reside in the same filesystem according to the manual page.
There is a known issue for special filesystems like procfs and sysfs that should be noted.
It should documented that the function may implicitly utilize reflinks and server-side copy.

This was requested in #93152 (comment).

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