feat: check for `eza` to use in `$ZINIT[LIST_COMMAND]` option

[vladdoster]

The exa project is unmaintained and development moved the eza fork, but as of 1707207983, eza does not release prebuilt macOS binaries unlike exa. To avoid unnecessarily breaking user configurations, exa has not been removed.

Types of changes

• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] Documentation change
• [X] New feature (non-breaking change which adds functionality)

Checklist:

• [X] All new and existing tests passed.
• [ ] I have added tests to cover my changes.
• [ ] I have updated the documentation accordingly.