implement dd

I've been working on a clone of dd for fun! It's pretty well developed, though nowhere near done; there's a lot of corner cases and tests that still need to be fleshed out.

links:
repository
crate

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[emanueleaina]

Implementation ongoing under #1861

[tertsdiepraam]

Implemented in #2474