🧹 Refactor independent_evidence.py to reduce deep nesting in classify()

[edithatogo]

🎯 What: The code health issue addressed was deep nesting in the classify function. Logic that verifies the result artifact's content and logic that verifies the acknowledgement and attestation bindings were extracted into separate helper functions.

💡 Why: The classify function had deeply nested blocks verifying different parts of the packet. By extracting these into helper functions, the main classify function becomes much flatter, easier to read, and more maintainable.

✅ Verification: Validated via black and ruff check. Ran the test suite (specifically tools/tests/test_independent_evidence.py) to confirm no functionality was broken.

✨ Result: Improved readability and maintainability of the classify function by reducing nesting levels.

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PR created automatically by Jules for task 13169709233483265967 started by @edithatogo

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