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.

tests/drivers/route1_seam_pacing_bug487_test.lua

@@ -46,7 +46,9 @@ return function(game)
         os.getenv("POKEPORT_DRIVER") == nil)
   check("no fast-forward multiplier is set",
         (tonumber(os.getenv("POKEPORT_SPEED")) or 1) == 1
-          and (game.save.options.speed or 1) == 1)
+          and (game.save.options.speedOverworld or 1) == 1
+          and (game.save.options.speedBattle or 1) == 1
+          and (game.save.options.speedMenu or 1) == 1)
   check("a window is up to watch (this is a visual call)",
         love.window ~= nil and love.window.isOpen and love.window.isOpen())
   U.log("MAX FPS reads", FrameCap.label(game.save.options.fpsCap),