Support for very deep file hierarchies

[panhania]

Currently we don't properly support certain pathological cases like described in uutils/coreutils#7376 since we use similar standard library primitives.

This is currently blocked at wrappers for *at POSIX functions (e.g. openat) not being in the standard library: rust-lang/rust#120426. Because it can take a very long time until this is implemented and stabilized, we could implement our own wrappers in the meantime.