Domains by length selection (-ln/--length flag)

**Description**

Print/dump domains by their length. Choose the characters length range (for example, less than 6, or maybe, 8).

Look at the existing CLI argument parsing and output formatting in the codebase. Identify where domains are currently printed or dumped. Add a new flag (e.g., -ln or --length) to accept a length range, filter the domains accordingly, and output them. Check for existing tests related to domain filtering or CLI flags to understand the testing pattern.

Rédigé par le modèle d'indexation à partir du texte de l'issue.