[CLI] Don't `exit()` when certain exceptions occur.

[tzarc]

Description

CLI code has been written under the assumption that it's run once from the terminal. In cases where it was originally deemed "annoying" to dump out an exception, a hard exit() was invoked instead.

This causes issue with CI, which temporarily loads/unloads the CLI modules. We get random unexplained failures as a result of the exit() calls. This introduces a maybe_exit which allows overriding by CI (later) and thus not killing the process invoking CI.

Types of Changes

• [ ] Core
• [ ] Bugfix
• [ ] New feature
• [x] Enhancement/optimization
• [ ] Keyboard (addition or update)
• [ ] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Checklist

• [x] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).