Standardize task run state conflict error response

[fat-catTW]

Update the Execution API response for task run state conflicts to use RFC 9457-style problem detail fields.

The response still keeps Airflow-specific fields like reason and previous_state, so clients can continue using machine-readable context while receiving a more standard error shape.

Updated the related API, Task SDK client, and supervisor tests to match the new response payload.

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[Andrushika]

This does not really match RFC 9457. It will create a nested response like this:
(since HTTPException is used here)

{
  "status_code": 409,
  "detail": {
    "type": "about:blank",
    "title": "Conflict",
    "status": 409,
    "detail": "TI was not ..."
  }
}

[Andrushika]

Hi! Please make sure every breaking change in the execution API has a corresponding Cadwyn migration. (Please follow contributing-docs/19_execution_api_versioning.rst)