- Rename `wd471` to` wPikachuSpawnStateFlags`, with `BIT_PIKACHU_SPAWN_*` bits
- Rename `wd492` to `wPikachuMapScriptFlags`, with `BIT_PIKACHU_MAP_*` bits
- Introduce `PIKAMOVEMENT_*` constants for `ApplyPikachuMovementData`
- Refactor `BillsHouse` scripts and Pikachu/Bill movement data