`Rating` already derived `PartialEq`, but that derive is only reachable
through `D: PartialEq` — and `ConstantDrift`, the crate's own only
`Drift` impl, did not satisfy it. So the derive was there and unusable.
Found by writing the comparison from a consumer's position rather than
reading the derive list.
`ConstantDrift`, `ConvergenceOptions` and `GameOptions` now derive
`PartialEq`. All three are pure configuration; comparing two is the
natural thing to want and nothing about them makes equality ambiguous.
`tests/trait_impls.rs` pins the surface, written the way the failure was
reported: a consumer struct that *holds* a `History` and derives
`Debug`. It also asserts `History`'s `Debug` summarises rather than
dumping its skill stores, so a future derive cannot quietly replace the
hand-written impl.
`Clone` on `History` stays off. It is a decision, not an omission: a
history owns every slice's skill store and arena, so cloning one is
proportional to the whole fit, and no consumer has wanted it.
Closes#76.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ
