Substrait literal conversion should preserve nested nullability #22095

Is your feature request related to a problem or challenge?

DataFusion’s Substrait consumer currently normalizes some nested literal fields to nullable when converting Substrait literals into ScalarValues.

This is intentional today because VirtualTable / Values consumption converts the schema and literal rows separately. DataFusion later materializes the values into Arrow arrays and builds a RecordBatch using the schema. Arrow requires nested field types to match exactly, including nullability, so a mismatch like this can fail even
when the value itself is valid:

  schema:  List(Field { name: "item", data_type: Int32, nullable: false })
  literal: List(Field { name: "item", data_type: Int32, nullable: true })

Describe the solution you'd like

Add an expected-type-aware Substrait literal conversion path.

For VirtualTable / Values, the consumer has access to the NamedStruct schema. When converting each literal row, pass the expected top-level Field into literal conversion, and recursively use the expected nested fields for Struct, List, and Map literals.

The existing schema-less literal conversion path should remain available for ordinary expression literals where no expected field/type is available.

Describe alternatives you've considered

No response

Additional context

No response