Enhancement

The enable_shared_scan feature ensures that data is evenly distributed across all scan operator drivers, addressing scenarios where the data output by IO tasks is uneven.

Currently, it is disabled by default due to a potential drawback: if the data output by IO tasks is minimal and can be handled by partial operators, distributing it across all operators may introduce unnecessary scheduling overhead without yielding any performance gains.

Nonetheless, prioritizing robustness, we should enable this feature by default and work on mitigating the associated performance drawbacks.