fix(expr): fix casting rules for struct (#7202)

Fix row type alignment. As mentioned by @xiangjinwu [here](#7189 (comment)):
> It is due to the fact that we do not allow casting between the same type, so the 2nd field fails to match interval to interval 😂

Thanks to @xiangjinwu for pointing out the quick fix.

Approved-By: xiangjinwu

e2e_test/batch/types/struct/struct_cast_2.slt.part

@@ -51,3 +51,15 @@ select row(1) < row(true);
 
 statement error
 select row(1) < row(1, 1);
+
+# Align row types
+query I
+select CASE WHEN false THEN ROW(1.1, INTERVAL '1') ELSE ROW(0, INTERVAL '1') END;
+----
+(0,00:00:01)
+
+# Align row types
+query I
+select CASE WHEN false THEN ROW(0, INTERVAL '1') ELSE ROW(1.1, INTERVAL '1') END;
+----
+(1.1,00:00:01)

src/frontend/planner_test/tests/testdata/struct_query.yaml

@@ -364,3 +364,9 @@
     CREATE TABLE a (c STRUCT<i STRUCT<a INTEGER>, j INTEGER>);
     INSERT INTO a VALUES (1);
   binder_error: 'Bind error: cannot cast type "integer" to "struct<i struct<a integer>,j integer>" in Assign context'
+- name: test struct type alignment in CASE expression
+  sql: |
+    select CASE WHEN false THEN ROW(0, INTERVAL '1') WHEN true THEN ROW(1.1, INTERVAL '1') ELSE ROW(1, INTERVAL '1') END;
+  logical_plan: |
+    LogicalProject { exprs: [Case(false:Boolean, Row(0:Int32::Decimal, '00:00:01':Interval), true:Boolean, Row(1.1:Decimal, '00:00:01':Interval), Row(1:Int32::Decimal, '00:00:01':Interval))] }
+    └─LogicalValues { rows: [[]], schema: Schema { fields: [] } }

src/frontend/src/expr/type_inference/cast.rs

@@ -154,7 +154,7 @@ fn cast_ok_struct(source: &DataType, target: &DataType, allows: CastContext) ->
             lty.fields
                 .iter()
                 .zip_eq(rty.fields.iter())
-                .all(|(src, dst)| cast_ok(src, dst, allows))
+                .all(|(src, dst)| src == dst || cast_ok(src, dst, allows))
         }
         // The automatic casts to string types are treated as assignment casts, while the automatic
         // casts from string types are explicit-only.