Deprecate multi-irb feature

Plan

• Print deprecation warnings on these commands: irb, jobs, fg, and kill in the next minor release
• Completely remove those commands in v2.0.0

Reasons

• It's concept highly overlaps with workspace commands like chws, pushws...etc.
• It spawns a new thread for every new new session, which conflicts with the upcoming irb-debug integration
• But most importantly, we can't find any practical use for this feature and the cost of maintaining its compatibility with other features is high
  • For example, it will require the solution of #650 to support multi-thread irb sessions too

Feedback wanted

If you use the multi-irb feature and don't want to see it deprecated from IRB, please leave a comment below to explain your use case of it. It will help us assess this plan.

Commencez par localiser les implémentations et la gestion des commandes pour irb, jobs, fg et kill, puis examinez comment les versions et les dépréciations d’IRB sont gérées. La tâche sera considérée comme terminée lorsque ces commandes afficheront un avertissement dans la prochaine version mineure et seront supprimées dans v2.0.0, avec les tests concernés mis à jour.