feat: add mysql test dispatch

Wires the test framework dispatch for the MySQL v4 adapter (soda-mysql,
landing in soda-extensions). Companion change to feature/mysql-support
in soda-extensions and soda-library.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: paulteehan

soda-tests/src/helpers/data_source_test_helper.py

@@ -335,6 +335,12 @@ def create(cls, test_datasource: str, name: str) -> DataSourceTestHelper:
             )
 
             return HanaDataSourceTestHelper(name)
+        elif test_datasource == "mysql":
+            from soda_mysql.test_helpers.mysql_data_source_test_helper import (
+                MySqlDataSourceTestHelper,
+            )
+
+            return MySqlDataSourceTestHelper(name)
         else:
             raise AssertionError(f"Unknown test data source {test_datasource}")