Support generic leaderboard views

[KyleHerndon]

Moves the commissioners-side generic leaderboard redesign from the archived commissioners repo into coworld-tools.

Summary:

• Adds commissioner-published generic leaderboards with selector axes, per-view axis values, and row columns.
• Keeps old rankings/table protocol compatibility behind TODO-delete shims.
• Builds round-complete leaderboard snapshots from current and recent results so EWMA stays commissioner-owned.
• Adds round_results_request / round_results_response plus RoundPlatformClient.get_round_results(...) so commissioners can fetch historical rows for EWMA or other time-window calculations.

Validation:

• uv run pytest tests/test_commissioner_strategies.py -q: 75 passed
• uv run python -m compileall commissioners tests/test_commissioner_strategies.py -q: passed
• uv run pytest tests/test_commissioner_websocket.py::test_round_platform_client_requests_round_results tests/test_commissioner_websocket.py::test_protocol_accepts_prefixed_round_public_id_and_episode_completed_response -q: 2 passed
• uv run python -m py_compile commissioners/common/protocol.py commissioners/common/server.py tests/test_commissioner_websocket.py: passed
• uv run ruff check commissioners/common/protocol.py commissioners/common/server.py tests/test_commissioner_websocket.py: unavailable, ruff is not installed in this repo env
• uv run pyright commissioners tests/test_commissioner_strategies.py: unavailable, pyright is not installed in this repo env
• timeout 90s uv run pytest tests/test_commissioner_websocket.py -q: timed out before producing output; the focused protocol/client tests above cover this change