Native `collect_set(struct)` aggregate crashes on spill emit

[hsiang-c]

Describe the bug

Native collect_set / collect_list over a struct with a non-nullable nested field aborts in GroupedHashAggregateStream::emit during spill:

ArrowError: column types must match schema types,
  expected List(Struct("colA": Boolean, ...))
  but found  List(Struct("colA": non-null Boolean, ...))  at column index 1

Call Stack: GroupedHashAggregateStream::emit (row_hash.rs:1134) ← spill ← try_update_memory_reservation. Fires only on the spill path.

Dependencies versions: DataFusion 54.1.0 / arrow 58.4.0.

Steps to reproduce

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Expected behavior

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Additional context

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