Fix disconnectObserverFromGroup using wrong lookup table

[C6H15]

In the prior fix State.entityToObservers was used and observer IDs matched against group IDs. This could skip exit callbacks when unsubscribing an observer from a group. The fix is to iterate through State.entityToGroups instead.

Test (Server)

--!strict
local QuickZone = require(workspace.QuickZone)

local Red = Color3.fromRGB(255, 0, 0)
local Blue = Color3.fromRGB(0, 0, 255)

local ZonePart = Instance.new("Part")
ZonePart.Anchored = true
ZonePart.CastShadow = false
ZonePart.CanCollide = false
ZonePart.Name = "Test"
ZonePart.Position = vector.zero
ZonePart.Size = vector.one * 20
ZonePart.Material = Enum.Material.ForceField
ZonePart.Color = Color3.fromRGB(0, 0, 255)
ZonePart.Parent = workspace

local function CreatePart(Color: Color3, Angle: number): BasePart
   local Part = Instance.new("Part")
   Part.Anchored = true
   Part.CastShadow = false
   Part.CanCollide = false
   Part.Position = vector.create(math.cos(Angle) * 5, 3, math.sin(Angle) * 5)
   Part.Size = vector.one * 2.5
   Part.Material = Enum.Material.SmoothPlastic
   Part.Color = Color
   Part.Parent = workspace
   return Part
end

local RedParts = {
   CreatePart(Red, 0),
   CreatePart(Red, math.rad(120)),
   CreatePart(Red, math.rad(240)),
}
local BlueParts = {
   CreatePart(Blue, math.rad(60)),
   CreatePart(Blue, math.rad(180)),
   CreatePart(Blue, math.rad(300)),
}

local Zone = QuickZone.Zone.fromPart(ZonePart)
local RedGroup = QuickZone.Group.new({
   ["entities"] = RedParts,
})
local BlueGroup = QuickZone.Group.new({
   ["entities"] = BlueParts,
})
local Observer = QuickZone.Observer.new({
   ["groups"] = {RedGroup, BlueGroup},
   ["zones"] = {Zone},
})

Observer:onEnter(function(Entity, Zone)
   if Entity:FindFirstChildOfClass("Highlight") == nil then
   	local Highlight = Instance.new("Highlight")
   	Highlight.FillTransparency = 0.75
   	Highlight.DepthMode = Enum.HighlightDepthMode.Occluded
   	Highlight.FillColor = Color3.fromRGB(0, 255, 0)
   	Highlight.Parent = Entity
   end
end)

Observer:onExit(function(Entity, Zone)
   local Highlight = Entity:FindFirstChildOfClass("Highlight")
   if Highlight ~= nil then Highlight:Destroy() end
end)

task.delay(5, function()
   local Count: number = 0
   Observer:unsubscribe(BlueGroup)
   for _, v in BlueParts do
   	if v:FindFirstChildOfClass("Highlight") == nil then continue end
   	Count += 1
   end
   if Count > 0 then
   	print(`Only {Count}/{#BlueParts} blue parts still have highlights after unsubscribing.`)
   else
   	print(`All highlights have been removed.`)
   end
end)