[AIP-94] Mark tasks CLI commands as migrated to airflowctl

[YAshhh29]

Add the @deprecated_for_airflowctl marker decorator to the 5 tasks CLI
commands that have airflowctl equivalents:

• tasks failed-deps
• tasks state
• tasks list
• tasks states-for-dag-run
• tasks clear

This follows the simplified marker-only direction described in #68402
(comment by @bugraoz93) and the same pattern as #68932 (variables) and
#68958 (config).

related: #68402

[boring-cyborg]

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[bugraoz93]

Thrse still need parity in airflowctl. Only a couple left but we should wait those for tasks. Thanks for the PR

[bugraoz93]

https://cwiki.apache.org/confluence/spaces/AIRFLOW/pages/382175838/AIP-94+Decouple+Remote+Commands+from+airflow+CLI+to+airflowctl#AIP94DecoupleRemoteCommandsfromairflowCLI(toairflowctl)-Whatchangedoyouproposetomake%3F

[YAshhh29]

Thanks for the review and the context! That makes sense — I'll keep this PR open so it's ready to merge as soon as the remaining [airflowctl tasks] commands land and parity is complete. Happy to help implement any of those if it'd be useful.