Fix World Each to iterate multiple archetypes (#174)

* Add tests for entity-child relationships and removal in world queries, fixed world_each

* Correct test case

---------

Co-authored-by: Marcus <ukendio@gmail.com>

jecs.luau

@@ -1995,6 +1995,7 @@ local function world_each(world: World, id): () -> ()
 			archetype = archetypes[archetype_id]
 			entities = archetype.entities
 			row = #entities
+			entity = entities[row]
 		end
 		row -= 1
 		return entity

test/tests.luau

@@ -900,20 +900,39 @@ end)
 
 TEST("world:children", function()
 	local world = world_new()
-	local e1 = world:entity()
+	local C = world:component()
-	local e2 = world:entity()
+	local T = world:entity()
-	local e3 = world:entity()
 
+	local e1 = world:entity()
+	world:set(e1, C, true)
+
+	local e2 = world:entity()
+
+	world:add(e2, T)
 	world:add(e2, pair(ChildOf, e1))
+
+	local e3 = world:entity()
 	world:add(e3, pair(ChildOf, e1))
 
-	for entity in world:children(pair(ChildOf, e1)) do
+	local count = 0
+	for entity in world:children(e1) do
+		count += 1
 		if entity == e2 or entity == e3 then
 			CHECK(true)
 			continue
 		end
 		CHECK(false)
 	end
+	CHECK(count == 2)
+
+	world:remove(e2, pair(ChildOf, e1))
+
+	count = 0
+	for entity in world:children(e1) do
+		count += 1
+	end
+
+	CHECK(count == 1)
 end)
 
 TEST("world:clear()", function()
@@ -1562,9 +1581,9 @@ TEST("repro", function()
 		local world = world_new()
 		local component1 = world:component()
 		local tag1 = world:entity()
-		
+
 		local query = world:query(component1):with(tag1):cached()
-		
+
 		local entity = world:entity()
 		world:set(entity, component1, "some data")