Bite-sized, TDD-style task breakdown for the second tier of the engine
redesign: introduce VarStore, Factor trait, BuiltinFactor enum, and
EpsilonOrMax schedule, then re-implement Game::likelihoods on top of
the new machinery. Internal-only refactor; public Game/History API
unchanged.
Acceptance: existing tests pass within ULP, iteration counts match T0,
no Batch::iteration regression vs T0 (~21.5 µs).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Anders Olsson
fa85bcee51