refactor: extract _add_test_tasks to reduce build_airflow_graph complexity

[Aaditya-git]

Summary

Closes #1943

build_airflow_graph had a cyclomatic complexity of 11, exceeding the ruff C901 limit of 10 and requiring a # noqa: C901 suppression comment.

This PR extracts the test-behavior branching block into a dedicated _add_test_tasks helper function, reducing build_airflow_graph's complexity from 11 to 9 and removing the suppression comment.

Changes

• cosmos/airflow/graph.py: new _add_test_tasks function handles both AFTER_ALL and BUILD/AFTER_EACH test behavior cases. build_airflow_graph now calls it in one line instead of ~40 lines of inline branching. The # noqa: C901 comment is removed.

No behavior changes

This is a pure refactor. All existing logic is preserved verbatim inside _add_test_tasks, the only difference is where the code lives. All existing tests for build_airflow_graph continue to cover the same behavior paths.

[pankajkoti]

Thanks for tackling #1943, @Aaditya-git, and apologies for the duplicated effort here.

This overlaps almost entirely with #2689, which was opened earlier (May 16) and is solving the same issue the same way: extracting the test-task branches into a new _add_test_tasks helper and removing the # noqa: C901. That PR has already been through a review round and, importantly, has been rebased on top of #2615 (Watcher depends on past), so its helper carries the tasks_map[f"{dbt_project_name}_test"] = test_task line that #2615 added. This branch predates that change, so as-is it would drop that line and regress the watcher's wait_for_downstream propagation.

To avoid two contributors maintaining the same refactor, I'm going to close this in favor of #2689. This isn't a reflection on the quality of your change, the approach is sound. Looking forward to your continued contributions to the project.