test: add complex cast SQL coverage

Add a SQL test resource that exercises nested struct, array, and array-of-struct casts.

Co-authored-by: Codex <codex@openai.com>

Author: manuzhang

spark/src/test/resources/sql-tests/expressions/cast/cast_complex.sql

@@ -0,0 +1,107 @@
+-- Licensed to the Apache Software Foundation (ASF) under one
+-- or more contributor license agreements.  See the NOTICE file
+-- distributed with this work for additional information
+-- regarding copyright ownership.  The ASF licenses this file
+-- to you under the Apache License, Version 2.0 (the
+-- "License"); you may not use this file except in compliance
+-- with the License.  You may obtain a copy of the License at
+--
+--   http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing,
+-- software distributed under the License is distributed on an
+-- "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+-- KIND, either express or implied.  See the License for the
+-- specific language governing permissions and limitations
+-- under the License.
+
+statement
+CREATE TABLE test_cast_complex(
+  id int,
+  struct_arr struct<items:array<int>,label:string>,
+  deep struct<outer:struct<middle:struct<value:string,flag:boolean>,numbers:array<string>>,note:string>,
+  arr_struct array<struct<id:int,score:string>>
+) USING parquet
+
+statement
+INSERT INTO test_cast_complex VALUES
+  (
+    1,
+    named_struct(
+      'items', array(1, 2, cast(null as int)),
+      'label', 'first'),
+    named_struct(
+      'outer',
+      named_struct(
+        'middle', named_struct('value', '1', 'flag', true),
+        'numbers', array('2', '3')),
+      'note', 'alpha'),
+    array(
+      named_struct('id', 1, 'score', '10'),
+      named_struct('id', 2, 'score', cast(null as string)))
+  ),
+  (
+    2,
+    named_struct(
+      'items', cast(array() as array<int>),
+      'label', cast(null as string)),
+    named_struct(
+      'outer',
+      named_struct(
+        'middle', named_struct('value', cast(null as string), 'flag', false),
+        'numbers', array(cast(null as string))),
+      'note', cast(null as string)),
+    array(named_struct('id', cast(null as int), 'score', '30'))
+  ),
+  (
+    3,
+    cast(null as struct<items:array<int>,label:string>),
+    cast(null as
+      struct<outer:struct<middle:struct<value:string,flag:boolean>,numbers:array<string>>,
+      note:string>),
+    cast(array() as array<struct<id:int,score:string>>)
+  ),
+  (
+    4,
+    named_struct(
+      'items', array(-1, 0, 2147483647),
+      'label', 'edge'),
+    named_struct(
+      'outer',
+      named_struct(
+        'middle', named_struct('value', '-4', 'flag', true),
+        'numbers', array('-5', '0')),
+      'note', 'omega'),
+    cast(null as array<struct<id:int,score:string>>)
+  )
+
+-- struct field containing an array
+query
+SELECT cast(struct_arr as struct<items:array<string>,label:string>), id
+FROM test_cast_complex
+ORDER BY id
+
+-- deeply nested struct to struct
+query
+SELECT cast(deep as
+  struct<outer:struct<middle:struct<value:int,flag:string>,numbers:array<int>>,note:string>), id
+FROM test_cast_complex
+ORDER BY id
+
+-- deeply nested struct to string
+query
+SELECT cast(deep as string), id
+FROM test_cast_complex
+ORDER BY id
+
+-- array of structs to array of structs
+query
+SELECT cast(arr_struct as array<struct<id:bigint,score:int>>), id
+FROM test_cast_complex
+ORDER BY id
+
+-- array of structs to string
+query
+SELECT cast(arr_struct as string), id
+FROM test_cast_complex
+ORDER BY id