Previously the upstream FurnaceStartSmeltEvent would default to the
recipes cooking time, ignoring any modifications from the furnace speed
multiplier.
While this works correctly for upstream, paper introduces the speed
multiplier API, which allows a different cook time from the one provided
by the recipe.
This commit now passes the modified cooktime to the furnace start smelt
event explicitly, instead of allowing the event to default to the
recipes cooking time, thus ensuring that the speed modifier is
respected.
Resolves: #6376
