datalad_next.patches.commanderror

Improve CommandError rendering and add returncode alias for code

This patch does two things:

It overwrites __repr__, otherwise CommandError` would use ``RuntimeError's variant and ignore all additional structured information except for .msg -- which is frequently empty and confuses with a CommandError('') display.

It adds a returncode alias for code. This unifies return code access between CommandError and Popen`-like objects, which usually have a returncode attribute.