Fix LIST type mods being duplicated

[Paliak]

Fixes #8971

Description of the problem being solved:

#8862 seems to have caused an issue where LIST type mods are duplicated due to how ModListClass:MergeMod handles them

PathOfBuilding/src/Classes/ModList.lua

Lines 48 to 59 in d2524f9

	function ModListClass:MergeMod(mod)
	if mod.type == "BASE" or mod.type == "INC" or mod.type == "MORE" then
	for i = 1, #self do
	if modLib.compareModParams(self[i], mod) then
	self[i] = copyTable(self[i], true)
	self[i].value = self[i].value + mod.value
	return
	end
	end
	end
	self:AddMod(mod)
	end

This PR adds a switch to ModListClass:MergeMod causing mods which cannot be merged to not be added.

[Wires77]

Revisiting this code when looking over this PR makes me realize there are a few more hidden gotchas here.

1. Making a mod unscalable in a LIST mod doesn't do anything. An example of this would be "banners also cause enemies to take (%d+)%% increased damage". This code only checks for unscalable at the LIST level, not for each subMod:

   PathOfBuilding/src/Classes/ModStore.lua

   Lines 37 to 50 in 78326a6

   	function ModStoreClass:ScaleAddMod(mod, scale, replace)
   	local unscalable = false
   	for _, effects in ipairs(mod) do
   	if effects.unscalable then
   	unscalable = true
   	break
   	end
   	end
   	if scale == 1 or unscalable then
   	self:AddMod(mod)
   	else
   	local scaledMod = copyTable(mod)
   	local subMod = scaledMod
   	if type(scaledMod.value) == "table" then

2. Unscaleable mods get added twice. I tested "take no extra damage from critical strikes" and saw the value double (even though there is a hard cap on a lot of these unscalable mods

In short, I'll merge this PR but I needed to write this down somewhere so it can be refactored again, with proper test cases added for all these corner cases.