Add airflowctl tasks clear command

[FrankYang0529]

• Add airflowctl tasks clear <dag_id>.
• Add TasksOperations.clear in operations.py (POST /dags/{dag_id}/clearTaskInstances), from which the CLI command is auto-generated.
• Make generated bool flags follow the ClearTaskInstancesBody field defaults.
• Accept --task-ids as comma-separated ids or a JSON list of task_id / [task_id, map_index].
• Mark the core CLI command with @deprecated_for_airflowctl("airflowctl tasks clear") and register it in test_command_deprecations.py.

Add TasksOperations.clear() in operations.py calling POST /dags/{dag_id}/clearTaskInstances. airflowctl tasks clear is auto-generated from it. Bool flags of ClearTaskInstancesBody follow the datamodel field defaults: a bare tasks clear dry-runs, --no-dry-run actually clears, and --run-on-latest-version keeps its tri-state fallback semantics. --task-ids accepts comma-separated ids or a JSON list of task_id / [task_id, map_index].

• closes: [AIP-94] airflowctl tasks: add clear command #66176
• related: [AIP-94] airflowctl command migration #68402

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

• Yes - Claude Code

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[henry3260]

reopen to trigger full ci test

[henry3260]

LGTM! need another pair of eyes