…62053)

## Description

`planner.plan()` now returns a tuple `(physical_plan, callbacks)` after
#61405. In this PR, I've updates the planner unit tests to unpack the
tuple instead of indexing into the result.

I'm doing this to make the return type a bit more explicit and readable.

## Related issues

Related to #61405

Signed-off-by: Balaji Veeramani <bveeramani@berkeley.edu>

## Description

In this PR, I've removed old callback registration APIs
(`get_execution_callbacks`, `add_execution_callback`,
`remove_execution_callback`) in favor of the new
`execution_callback_classes` property on `DataContext`.

This is part of a larger effort to avoid storing callback instances in
`DataContext` since they might be shared across dataset executions. The
new implementation re-constructs the callbacks for each execution and
directly passes them into the executor as a constructor argument. This
makes the data flow much more explicit and easier to reason about.

## Related issues

Follow-up to #61405.

Signed-off-by: Balaji Veeramani <bveeramani@berkeley.edu>

…62055)

## Description

In this PR, I've removed old callback registration APIs
(`get_execution_callbacks`, `add_execution_callback`,
`remove_execution_callback`) in favor of the new
`execution_callback_classes` property on `DataContext`.

This is part of a larger effort to avoid storing callback instances in
`DataContext` since they might be shared across dataset executions. The
new implementation re-constructs the callbacks for each execution and
directly passes them into the executor as a constructor argument. This
makes the data flow much more explicit and easier to reason about.

## Related issues

Follow-up to ray-project#61405.

Signed-off-by: Balaji Veeramani <bveeramani@berkeley.edu>