Per-category GAME SPEED: overworld/battle/menu + core.logic_speed hook (RFC 0007)

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.

src/battle/BattleState.lua

@@ -37,6 +37,12 @@ local BattleState = {}
 BattleState.__index = BattleState
 BattleState.isOpaque = true
 
+-- Category identity for per-category GAME SPEED (RFC 0007), the same
+-- style OverworldController.isOverworld already uses. Every battle --
+-- wild, trainer, link, safari, the old-man demo -- is this metatable, so
+-- Game.speedCategoryInStack needs no special-casing beyond this one flag.
+BattleState.isBattle = true
+
 function BattleState:romText(label, fallback, ...)
   return romText(self.data, label, fallback, ...)
 end