Add "Validation Only" command to the mmg CLI

[ryul1206]

Is your feature request related to a problem? Please describe.
The current mmg CLI generates new files while outputting validation results. However, this can be inefficient in cases where only validation results are needed. This feature request aims to solve this issue.

Describe the solution you'd like
Add a new option to the mmg CLI that enables validation only, which will output validation results without generating new files. If the validation is successful, the CLI will raise SystemExit(0) to indicate success. If the validation fails, the CLI will raise SystemExit(1) to indicate a failure.

Describe alternatives you've considered
N/A

Additional context
N/A

[stale]

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