Fix portability of `sendfile(2)` support detection for Lustre filesystems

Bug report

Bug description:

On Lustre on Linux (specifically the AWS implementation) there is a rare and difficult to reproduce failure of shutil.copyfile in its sendfile(2) fast path because the syscall returns ENODATA. The situation is recoverable by falling back to the standard read/write file copy (patch forthcoming).

Reproducing the bug requires the filesystem to be in a specific state which I have not been able to reproduce at will but we've seen it on occasions by multiple users. Additionally similar bug has been seen on rust fs::copy which similarly does not trap the ENODATA error.

Following is sufficient to reproduce bug for the specific (rare) file that fails:

import shutil
shutil.copyfile('src', 'dst')

error:

sent = os.sendfile(outfd, infd, offset, blocksize)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 61] No data available: '/shared/fsx1/filename' 

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-139417

Beginne beim sendfile-Schnellpfad von shutil.copyfile und prüfe, wie Fehler von os.sendfile behandelt werden. Reproduziere den Fehler mit shutil.copyfile('src', 'dst') auf dem betroffenen Dateisystem; erledigt ist dies, wenn ein ENODATA-Fehler auf den standardmäßigen Lese-/Schreib-Kopierpfad zurückfällt.