Implement XA Support for DB2

[rrobetti]

Follow the approach in PR #68 (PostgreSQL XA support) to add XA (distributed transaction) support for DB2 in the integration test suite.

What to do:

• Update the XADataSourceFactory to fully implement createDB2XADataSource (see how it's done for PostgreSQL in the PR)
• Update DB2 integration tests: parameterize with both isXA=false and isXA=true in the relevant CSV files and test classes, as done for PostgreSQL
• Ensure tests use TestDBUtils.createConnection() to properly handle XA
• Validate XA functionality by running the tests in both JDBC and XA modes

References:

• PostgreSQL implementation: PR #68
• XA support guide

Keep the issue focused on DB2 only. Use the links above for detailed instructions and examples.

[ignorant05]

@rrobetti can you assign me this too ?