[Variant] Support composite typed_value values in VariantArray::try_value

[sdf-jkl]

Is your feature request related to a problem or challenge?

VariantArray::try_value can materialize primitive typed_value values but not legal shredded Struct or List values.

#10597 prevents these values from being silently reported as Variant::Null, but callers still cannot retrieve the complete row as a Variant without unshredding the array first.

Describe the solution you'd like

Support reconstructing perfectly and partially shredded Struct/List values in try_value.

This likely requires an owned or COW representation because composite values must be encoded into new buffers, while Variant currently borrows its encoded bytes.

Describe alternatives you've considered

Call unshred_variant on the complete array before accessing individual values. This works but requires array-level reconstruction when only one row may be needed.

Additional context

• [Variant] VariantArray::value silently returns Variant::Null for unimplemented typed_value types in release builds #10597
• Current unsupported arm: https://github.com/apache/arrow-rs/blob/main/parquet-variant-compute/src/variant_array.rs#L1126