GameSpeed is a single fast-forward multiplier applied uniformly to the
whole logic clock -- overworld walking, menu navigation and battle turns
all scale together. A player who wants 4X battles but 1X overworld (so a
cutscene or NPC dialogue doesn't blur past) has no way to get both.
Splits save.options.speed into speedOverworld/speedBattle/speedMenu, each
cycling independently, with an automatic migration so an existing save's
speed choice carries over. Game.speedCategoryInStack resolves which
category is active by walking the state stack (the same idiom
wideBattleInStack/fillScaleInStack already use), so a menu opened mid-
battle inherits battle speed rather than resetting to whatever "menu"
defaults to. Adds a new core.logic_speed hook so a mod can read or
override the resolved multiplier for the current frame regardless of
which category produced it, sitting after the link-play and run-argument
overrides so neither is a seam a mod can defeat.
RFC 0007 status: Proposed.