fix: use direct construction for JustifiedSlots

[tcoratger]

Summary

• Replace JustifiedSlots(data=[]).model_copy(update={"data": [...]}) with JustifiedSlots(data=[...]) across 8 occurrences in test_justification.py
• The model_copy pattern bypassed Pydantic validation, leaving a mutable list instead of the expected immutable tuple
• Direct construction is simpler and produces correctly validated data

Test plan

• uvx tox -e all-checks — all green

🤖 Generated with Claude Code

[tcoratger]

Closing: the model_copy pattern is intentional. The state transition function builds justified_slots via model_copy internally, which stores data as a list. Direct construction produces a tuple, causing equality mismatches. The fix needs to address the systemic list/tuple inconsistency in model_copy across the codebase first.