🧪 Add tests for changes_to_markdown in diff module

[edithatogo]

🎯 What: Added a unit test (test_changes_to_markdown_with_changes) to test the functionality of changes_to_markdown when there are actual parameter changes present.
📊 Coverage: The previously untested code branch handling the formatting of the markdown table has now been covered by testing value_change and removed_parameter mock objects.
✨ Result: Test coverage for contracts/tools/src/pic_contracts/diff.py has improved to 94%, filling the gap in validating the markdown generation function.

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PR created automatically by Jules for task 12426294842138946650 started by @edithatogo

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