Bug Description

When calling transform() on an IncrementalExecutionResultImpl, the method returns an IncrementalExecutionResult of the correct type, but loses the incremental-specific field values (incremental, hasNext, incrementalPublisher).

Expected Behavior

The transform() method should preserve both the incremental result type AND its specific field values.

Current Behavior

The transformed result is correctly typed as IncrementalExecutionResult but the incremental data fields are lost/null.

Reproduction

ExecutionResult incrementalResult = IncrementalExecutionResultImpl
    .newIncrementalExecutionResult()
    .incremental(List.of(DeferPayload.newDeferredItem().data("hello").build()))
    .build();

var transformedResult = incrementalResult.transform(builder -> builder.addExtension("key", "value"));

// transformedResult is correctly IncrementalExecutionResult, but incremental data is lost
assert transformedResult instanceof IncrementalExecutionResult; // PASSES
IncrementalExecutionResult incResult = (IncrementalExecutionResult) transformedResult;
assert incResult.getIncremental() != null; // FAILS - incremental data is lost

Impact

This breaks the contract that transform() should preserve all result data while allowing modifications. Users lose incremental payloads when transforming results.