Expand description
Save schema V3 — drops goldens_since_green_coin.
V3’s only persisted-shape change vs V2 is the removal of the Green Coin
pity counter. The Vec-based powerup refactor (#25) replaced the pity
mechanic with per-kind cooldown clocks (one for each PowerupKind),
all of which are #[serde(skip)]. The pity counter became dead weight
on disk — a field present in every V2 save that the live state doesn’t
consult anymore. V3 drops it.
Once V3 is on main this file is FROZEN: subsequent schema changes
go in v4.rs together with a From<GameStateV3> conversion.
Each persisted enum/struct re-uses V2’s frozen copies (modifier source, effect, duration, modifier, fingerer state, buff). The struct-level shape change is small enough that re-vendoring the inner types would be pure noise.