cp: Support copying FIFOs with -r

[water-ghosts]

This pull request handles the GNU test cp/special-f, which uses cp -R fifo e to copy a FIFO.

I noticed that this test was not only failing, but taking about 4 minutes to fail, which is an appreciable amount of the total test suite time. If I understand this correctly, uutils ignored the -r flag and tried to copy the contents of the (empty) FIFO instead of the FIFO itself; it kept waiting for something to read until eventually timing out.

Since Rust doesn't natively support copying FIFOs (see issue #1710), I implemented this by creating a new FIFO with the destination name. There's definitely room to improve on this (e.g. copying file permissions), but I experimented a bit and it doesn't seem like GNU's copies are much more than new instances, so I don't think this is too bad.

I'm still pretty new to this project and Rust in general, so let me know if there's a better way to go about this. I'm happy to either revise this PR or close it and create an issue if you'd prefer to solve this another way 🙂

[sylvestre]

excellent:
Changes from main: PASS +3 / FAIL -3 / ERROR +0 / SKIP +0