Use uutils/coreutils for cross platform commands?

It's all in the title really. Rust [coreutils](https://github.com/uutils/coreutils) are rapidly becoming the standard in Linux and are now even [available for Windows](https://learn.microsoft.com/en-us/windows/core-utils/overview).

The crate already builds as wasm ([and can run in the browser](https://uutils.org/playground/)!). Since this project already does create a was, for the shell parser, it might not be that big of a lift to include `coreutils` as well.

This would replace a number (all?) custom implementations of commands with the `coreutils`, thus providing wider and more accurate support for flags. Potentially even speed benefits. More crucially it would close the wide gap of commands still missing.

This is a proposal/thought. If you are interested I might be able to work on it.

The issue names no files or tests; start by inventorying the project's custom command implementations and reviewing how its shell parser is built for wasm. Define the command scope and integration approach before attempting the replacement, with completion requiring the selected commands to work across the stated Linux, Windows, and wasm targets.

Written by the indexing model from the issue text.