Move CloudComposerExternalTaskSensor task-id wrapping out of __init__

[KingLizard1020]

CloudComposerExternalTaskSensor inspected templated task-id arguments in __init__: it converted an empty list to unset, wrapped composer_external_task_id into composer_external_task_ids, and used truthiness to choose Dag vs task state validation.

Those value reads now run after rendering in poke() / execute() via _normalize_external_task_ids. An empty composer_external_task_ids=[] is treated as unset before exclusivity and dag-vs-task state checks, matching the previous constructor. Duplicate-state checks on non-templated allowed_states / skipped_states / failed_states stay in __init__. The exemption entry is removed.

related: #70296

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Was generative AI tooling used to co-author this PR?

• Yes — Cursor

Generated-by: Cursor following the guidelines

[boring-cyborg]

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[Vamsi-klu]

The exemption is removed, not broadened. IDs are assigned verbatim in init and wrapped after render in poke / execute. No template-field hole that I can see.