Run sqllogictests (subset) through distributed execution example

[Dandandan]

Is your feature request related to a problem or challenge?

Follow-up to #23303 (prototype in #23282).

The in-process distributed execution example validates the stage/serialize/isolate contract with a handful of handwritten integration tests (joins, sorts, multi-stage aggregates). That is enough to demonstrate the model, but the coverage is only as broad as the queries someone thought to write.

Describe the solution you'd like

Run (a subset) of the sqllogictests through the distributed execution example, so each query is planned normally, split into stages, serialized via datafusion-proto, executed as isolated tasks over the in-memory exchange, and its results compared against the expected output.

Describe alternatives you've considered

• Keep only handwritten integration tests in the example crate: coverage stays narrow and grows only when someone remembers to add a case.

Additional context

• Depends on Add an example of an in-process model of distributed execution #23303; working prototype of the execution harness in Add an example of an in-process model of distributed execution #23282.
• Prior art: datafusion-distributed and Ballista both maintain their own differential testing against DataFusion; running the in-tree sqllogictests through an in-tree harness shortens that feedback loop to a single repo.