refactor: Consolidate struct casting logic into nested_struct module

Remove duplicate struct_cast.rs module and use the existing
nested_struct::cast_struct_column implementation instead. This
eliminates code duplication and provides a single source of truth
for struct field-by-name casting logic.

Changes:
- Add public cast_struct_array_by_name wrapper in nested_struct.rs
- Update columnar_value.rs to use nested_struct::cast_struct_array_by_name
- Update scalar/mod.rs to use nested_struct::cast_struct_array_by_name
- Remove struct_cast module from lib.rs
- Delete datafusion/common/src/struct_cast.rs

Benefits:
- Single implementation to maintain and test
- Consistent behavior across all struct casting operations
- Reduced maintenance burden for future bug fixes
- Better code cohesion in nested_struct module

Author: kosiew

datafusion/common/src/lib.rs

@@ -57,7 +57,6 @@ pub mod rounding;
 pub mod scalar;
 pub mod spans;
 pub mod stats;
-pub mod struct_cast;
 pub mod test_util;
 pub mod tree_node;
 pub mod types;

datafusion/common/src/nested_struct.rs

@@ -165,6 +165,32 @@ pub fn cast_column(
     }
 }
 
+/// Cast a struct array to another struct type by aligning child arrays using
+/// field names instead of their physical order.
+///
+/// This is a convenience wrapper around [`cast_struct_column`] that accepts
+/// `Fields` directly instead of requiring a `Field` wrapper.
+///
+/// See [`cast_column`] for detailed documentation on the casting behavior.
+///
+/// # Arguments
+/// * `array` - The source array to cast (must be a struct array)
+/// * `target_fields` - The target struct field definitions
+/// * `cast_options` - Options controlling cast behavior (strictness, formatting)
+///
+/// # Returns
+/// A `Result<ArrayRef>` containing the cast struct array
+///
+/// # Errors
+/// Returns an error if the source is not a struct array or if field casting fails
+pub fn cast_struct_array_by_name(
+    array: &ArrayRef,
+    target_fields: &arrow::datatypes::Fields,
+    cast_options: &CastOptions,
+) -> Result<ArrayRef> {
+    cast_struct_column(array, target_fields.as_ref(), cast_options)
+}
+
 /// Validates compatibility between source and target struct fields for casting operations.
 ///
 /// This function implements comprehensive struct compatibility checking by examining:

datafusion/common/src/scalar/mod.rs

@@ -3708,7 +3708,7 @@ impl ScalarValue {
         // Use name-based struct casting for struct types
         let cast_arr = match (scalar_array.data_type(), target_type) {
             (DataType::Struct(_), DataType::Struct(target_fields)) => {
-                crate::struct_cast::cast_struct_array_by_name(
+                crate::nested_struct::cast_struct_array_by_name(
                     &scalar_array,
                     target_fields,
                     cast_options,

datafusion/common/src/struct_cast.rs

@@ -325,7 +325,7 @@ fn cast_array_by_name(
 
     match (array.data_type(), cast_type) {
         (DataType::Struct(_source_fields), DataType::Struct(target_fields)) => {
-            datafusion_common::struct_cast::cast_struct_array_by_name(
+            datafusion_common::nested_struct::cast_struct_array_by_name(
                 array,
                 target_fields,
                 cast_options,