Add test for VQA generation

[Copilot]

Overview

This PR implements test_generate_vqa.py to provide e2e test coverage for VQA (Visual Question Answering) generation functionality.

Changes

Added tests/e2e_tests/test_generate_vqa.py following the same pattern as existing e2e tests (referenced from test_generate_aggregated.py).

Test Coverage

The test verifies that VQA generation:

• Executes successfully using vqa_config.yaml configuration
• Creates the expected output directory structure (data/graphgen/)
• Saves the configuration file in the run folder
• Generates JSON output files with valid data
• Produces log files for debugging

Implementation Details

The test follows the established e2e testing pattern in the repository:

• Uses pytest's tmp_path fixture for isolated test execution
• Runs the generation via subprocess to test the full CLI workflow
• Validates all expected output artifacts are created
• Checks JSON output structure (must be a non-empty list)

This completes the e2e test suite for all generation modes (atomic, aggregated, multi-hop, CoT, and now VQA).

Security

CodeQL analysis passed with 0 alerts.

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature] add test for vqa generation</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
test for vqa generation

Describe the solution you'd like
implement test_generate_vqa.py, reference: https://github.com/open-sciencelab/GraphGen/blob/main/tests/e2e_tests/test_generate_aggregated.py
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #71

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