test: improve test coverage for archive scanners (tar, zip, 7z)

[mldangelo]

Description

Improve test coverage for the archive scanner family: tar_scanner, zip_scanner, and sevenzip_scanner. These scanners handle nested model files inside archives and need thorough edge case testing.

Suggested test cases

• Archives containing multiple model files of different formats
• Deeply nested archives (archive within archive)
• Archives with symbolic links (security-relevant)
• Archives with path traversal attempts (e.g., ../../etc/passwd)
• Empty archives
• Corrupted/truncated archives
• Archives with very long filenames

References

• modelaudit/scanners/tar_scanner.py
• modelaudit/scanners/zip_scanner.py
• modelaudit/scanners/sevenzip_scanner.py
• tests/scanners/test_tar_scanner.py — existing tests to extend
• tests/scanners/test_zip_scanner.py — existing tests to extend
• docs/agents/testing.md — test patterns guide

Getting started

uv sync --extra all-ci
uv run pytest tests/scanners/test_tar_scanner.py tests/scanners/test_zip_scanner.py -v

Acceptance criteria

• At least 3 new test cases per scanner
• Tests cover at least one security-relevant edge case
• All tests pass: uv run pytest -n auto -m "not slow"