* Add a precondition to prevent the parsing of a command that has itself as its subcommand.
This avoids the infinite recursion that causes a crash and shows the user a meaningful error message.
Fixes: https://github.com/apple/swift-argument-parser/issues/192
* Fix the detection of a command that has itself as its subcommand
- The recursion detection now works for both the root command and its subcommands
- Add a test to shows that the fix works
* Fix typo in TreeTests