Use stat to retain file permissions when copying files

[lamcw]

With stat instead of chmod, this should improve the performance of copying many files with cp as chmod runs multiple syscalls when changing permissions.

Would be great if I can get your help to test these changes on Linux as well!

This is an alternative solution to #258.

Closes #256.

[benradf]

I gave it a try on Linux and it seems to work fine 👍

One thing that I think is okay but wanted to explicitly call out – the file copies will not retain exactly the same permissions as the originals now that we're no longer using chmod --reference. In practice I don't think this will matter though.

[aherrmann]

Thank you @lamcw for contributing this!
And thanks @benradf for looking into this and the alternative approach!

LGTM

Also pinging @guibou who had the original use-case for preserving the executable bit. Please let us know if this change causes any issues for your use-case.