fix(csharp): use predetermined type per info code in BuildGetInfoResult

VendorSql → bool, all others → string. The union type is determined
by the code, not by runtime type inspection of the value.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: msrathore-db

csharp/src/Hive2/MetadataSchemaDefinitions.cs

@@ -332,14 +332,18 @@ internal static IArrowArrayStream BuildGetInfoResult(
             {
                 infoNameBuilder.Append((uint)code);
 
+                // Union type is predetermined per info code:
+                // VendorSql → bool, all others → string
+                bool isBoolCode = code == AdbcInfoCode.VendorSql;
+
                 if (values.TryGetValue(code, out object? val) && val != null)
                 {
-                    if (val is bool boolVal)
+                    if (isBoolCode)
                     {
                         typeBuilder.Append(boolValTypeId);
                         offsetBuilder.Append(offset++);
                         stringInfoBuilder.AppendNull();
-                        booleanInfoBuilder.Append(boolVal);
+                        booleanInfoBuilder.Append(val is bool b && b);
                     }
                     else
                     {