maelstrom-linux should be IO-safe

[nfachan]

See: https://rust-lang.github.io/rfcs/3128-io-safety.html
And: rust-lang/rust#87074
And: nix-rust/nix#1750

Our maelstrom-linux APIs are no IO-safe.

One problem we face is that the library is no_std, or at least can be no_std. The new file descriptor types introduced to help with IO-safety are only in std. We could probably create our own similar types. Or we could look to see if there's a generic way we could implement the appropriate functions that would work for both std and no_std.