Fix only_new clear missing new tasks after a 'run on latest version' clear

[pulaksaha143]

Resolves #71455.

Problem

When a user clears a DagRun with run_on_latest_version=True, the created_dag_version_id column is updated to the latest version. Later, if the user performs a clear with only_new=True, the _get_new_task_ids function diffs the latest DAG's task IDs against the task IDs from the version referenced by created_dag_version_id. Because this pointer has mutated, it incorrectly detects an empty diff and silently skips creating actual new tasks.

Solution

Instead of relying on the mutable created_dag_version_id, we now directly query the database for the actual TaskInstance rows associated with the DagRun. We diff these existing task IDs against the latest DAG's task IDs to accurately inject genuinely new tasks.

Also includes an automated test asserting correct behavior when created_dag_version_id has been updated.