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

从 shutil.copyfile 的 sendfile 快速路径开始，检查如何处理 os.sendfile 错误。在受影响的文件系统上使用 shutil.copyfile('src', 'dst') 重现该故障；当 ENODATA 故障回退到标准的读/写复制路径时，即表示完成。