Support multiple leaderboard tables

[KyleHerndon]

Summary

• add table-native rank_division responses with a TODO: delete rankings compatibility shim
• let ruleset_strategy scoring config declare multiple leaderboard tables over arbitrary score keys, half-lives, and lookback windows
• serialize primary table rankings for legacy callers while returning all configured tables

Validation

• uv run pytest tests/test_commissioner_strategies.py -q
• uv run python -m compileall commissioners tests/test_commissioner_strategies.py -q

Notes

• No repo lint command is defined in pyproject/README/repo config.
• Broader pytest runs reached the existing slower websocket/Docker coverage and hung in this environment after the strategy tests completed, so I stopped them.