Fix null value for summary counts in evaluation result converter

[YoYoJa]

Description

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR adds null/NaN safety checks to evaluation summary calculation logic. The changes ensure that null or NaN values in model usage statistics and testing criteria results are properly handled rather than causing errors or corrupting summary data.

Key changes:

• Added _is_none_or_nan() checks before accumulating token counts and criteria statistics
• Refactored inline conditional expressions into explicit variable assignments with null/NaN validation
• Updated test data to reflect proper handling of null values in evaluation results

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
_evaluate.py	Added null/NaN safety checks for model_name, token counts, and testing criteria statistics
evaluation_util_convert_old_output_test.jsonl	Updated test data with additional violence evaluator fields and sample data
evaluation_util_convert_expected_output.json	Updated expected output to include new fields and corrected error message percentages
evaluation_util_convert_error_summary.json	Updated error summary to reflect partial completion (50% vs 100% failure)