* fix: don't invoke asdf inside asdf commands
Recursive calls have a number of disadvantages:
* Poorer performance since each invocation spawns and new process and re-executes all the code in bin/asdf
* Makes debugging more difficult
* More likely to introduce subtle bugs and the possibility for infinite loops
* Ban `ls` command
* Update banned commands test so it only checks bash and sh files
* Only allow `ls` for resolving symlinks
* Replace `ls` commands with `find`
