T-469 Prepare NumerAPI 3.0 multiplier removal

[numerai-hosted-agent-bot]

Summary

• prepare NumerAPI 3.0.0 by removing the six deprecated Corr/MMC multiplier projections from list_rounds()
• preserve the full exact-identity roundScoreConfigs return surface for Classic, Signals, and Crypto
• remove compatibility-only selection code/tests and update the migration docs and changelog

Hold / release blockers

• Draft only: do not merge, tag, or publish NumerAPI 3.0.0 before August 28, 2026.
• Do not make this mergeable until the T-469 public forum announcement URL/date is recorded.
• After the gated package publication, update the monorepo integration-test pin from 2.24.0.dev1 to 3.0.0 before the API removal PR merges.

Validation

• .venv/bin/python -m pytest --import-mode=append tests/ --cov=./ --cov-report=xml (58 passed, 6 skipped)
• .venv/bin/ruff check numerapi
• PATH="$PWD/.venv/bin:$PATH" make -C docs clean html (passes with two pre-existing Sphinx configuration warnings)
• .venv/bin/python setup.py --version (3.0.0)

Linear: T-469

[ndharasz]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: 7e91c46a25

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[numerai-hosted-agent-bot]

Release blocker found while updating T-469: tag 3.0.0.dev0 points to a35dbddf, whose setup.py sets numerapi_version = "3.0.0". The tag workflow will therefore build stable 3.0.0, while the requested 3.0.0.dev0 artifact is not available on PyPI. Please correct the package version/tag before publication (or explicitly revise the release plan); monorepo lock/pin updates cannot complete until the requested artifact exists. The August 28 stable-release gate remains recorded on monorepo PR #1142.