Command stepping

## What problem does this solve or what need does it fill?

Currently only systems can be stepped through.
With the arrival of hooks the command ecosystem will be a lot more active and prone to infinite recursion through self-queuing commands.
While this cannot be easily prevented, tooling can be provided to debug the issue.

## What solution would you like?

Ability to step through queued commands during `flush_commands` execution.
Human-readable command identifiers.
Similarly to systems, ability to always skip/run certain command types.

## What alternative(s) have you considered?

None

## Additional context

None