Remove flakiness and re-enable test 06 (tests/06_creating_dsl.js)

Test 06 (`tests/06_creating_dsl.js`) was temporarily skipped due to flakiness:
- The test is currently disabled with `@disabled: true`
- It covers creating DSL elements, setting class attributes, building associations, and model validation.

**Task:**
- Investigate and resolve the sources of flakiness affecting this test.
- Re-enable test 06 by removing the `@disabled` flag in the test file.
- Ensure the test passes reliably on local and CI runs.

Relevant code snippets:
[tests/06_creating_dsl.js](https://github.com/AToMPM/atompm/blob/e988b5abcf962960c7bc5066aea9cfa2fabe7c1d/tests/06_creating_dsl.js)
```javascript
// TODO: temporarily disable this test for CI and local runs; re-enable after fixing flakiness
module.exports = {
'@disabled': true,
...
}
```

Example involved in test operations:
- Class and attribute creation
- Model validation
- Association/inheritance creation

**Please review Nightwatch configuration and test utilities for potential timing or environment causes.**

---
Labels: Test/CI/CD, bug
Issue type: Bug

Start with tests/06_creating_dsl.js and run the disabled test to reproduce its flakiness. Review the Nightwatch configuration and test utilities for timing or environment causes, then verify the test passes reliably in local and CI runs after re-enabling it by removing @disabled.

Written by the indexing model from the issue text.