Add tests for mssql/base.py utility functions

- Add test_base.py with 45 tests covering:
  - encode_value()
  - encode_connection_string()
  - prepare_token_for_odbc()
  - handle_datetimeoffset()
  - DatabaseWrapper._is_driver_not_found_error()
- Add extras_require[test] with unittest-xml-reporting for Python 3.12+

Author: bewithgaurav

setup.py

@@ -49,6 +49,9 @@
         'pyodbc>=3.0',
         'pytz',
     ],
+    extras_require={
+        'test': ['unittest-xml-reporting>=3.2.0'],
+    },
     package_data={'mssql': ['regex_clr.dll']},
     classifiers=CLASSIFIERS,
     keywords='django',