Fix XMLType return value retrieval for Oracle 12c+

The return_variable_value method also needs to handle
OPAQUE/XMLTYPE data_type when reading back XMLType function
return values and output parameters.

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

Author: yahonda

lib/plsql/procedure_call.rb

@@ -517,8 +517,8 @@ def return_variable_value(argument, argument_metadata)
         when "PL/SQL BOOLEAN"
           numeric_value = @cursor[":o_#{argument}"]
           numeric_value.nil? ? nil : numeric_value == 1
-        when "UNDEFINED"
-          if argument_metadata[:type_name] == "XMLTYPE"
+        when "UNDEFINED", "XMLTYPE", "OPAQUE/XMLTYPE"
+          if argument_metadata[:type_name] == "XMLTYPE" || argument_metadata[:data_type] =~ /XMLTYPE/
             @cursor[":o_#{argument}"]
           end
         else