GH-73991: Add pathlib.Path.copy()

[barneygale]

Add a Path.copy() method that copies the content of one file to another.

This method is similar to shutil.copyfile() but differs in the following ways:

• Uses fcntl.FICLONE where available (see shutil: add reflink=False to file copy functions to control clone/CoW copies (use copy_file_range) #81338)
• Uses os.copy_file_range where available (see Use copy_file_range() in shutil.copyfile() (server-side copy) #81340)
• Uses _winapi.CopyFile2 where available, even though this copies more metadata than the other implementations. This makes WindowsPath.copy() more similar to shutil.copy2().

The method is deliberately less specified than the shutil functions to allow OS-specific optimizations that might copy more or less metadata.

Incorporates code by @illia-v and @giampaolo from #81338 and #93152 respectively.

• Issue: Support moving across filesystems in pathlib.Path, as shutil.move() does #73991

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📚 Documentation preview 📚: https://cpython-previews--119058.org.readthedocs.build/

[barneygale]

Marking this PR as a draft, because I think we'll need to introduce os.copy() first.

[zooba]

Just some thoughts, nothing I'd necessarily block the PR on. I like the way it looks overall!

[zooba]

Looks fine to me, but I only quickly reskimmed it. I'll be away for the next few days, so don't wait for me if you guys think it's ready.