Handle empty fastqc reports

[Ulthran]

Summary

• allow the fastqc report script to write an empty report when no per-base sequence quality data is available

Testing

• black .
• pytest tests/unit/
• pytest tests/e2e/test_sunbeam_run.py::test_sunbeam_run_with_single_end_reads (fails: conda not installed)

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Codex Task

[Copilot]

Pull request overview

This PR adds graceful handling for empty FastQC reports when no per-base sequence quality data is available. Instead of failing when attempting to concatenate an empty list, the script now writes an empty report with appropriate logging.

Key Changes

• Added a check for empty quality_list after filtering out None values
• When no quality data is found, the script logs a message and writes an empty DataFrame to the output file
• Early return prevents pandas.concat from attempting to process an empty list

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[Copilot]

The new empty report handling logic lacks test coverage. Consider adding unit tests to verify:

1. The behavior when all input reports return None from parse_fastqc_quality (empty quality_list)
2. That an empty DataFrame is correctly written to the output file
3. That the appropriate log message is written

Similar workflow scripts like preprocess_report.py have comprehensive unit tests in tests/unit/test_preprocess_report.py. Consider adding a tests/unit/test_fastqc_report.py file with tests for this new functionality.