Perf: allocation-free ItemSize/ItemAdd/IsMouseHoveringRect/GetColorU32/RenderArrow, @native on hot UI paths; t_drawhash output-equivalence check

tools/test/scripts/t_drawhash.luau

@@ -0,0 +1,29 @@
+-- Prints one checksum of all draw data (vertices, indices, clip rects) per run, with scripted mouse input.
+-- Use to prove an internal rewrite renders identically: run before/after with the same --open-only and compare.
+local G = require(game:GetService("ReplicatedStorage"):WaitForChild("ImGui"))
+local ImGui = G.ImGui
+ImGui.CreateContext()
+G.ImGui_ImplRoblox.Init()
+G.ImGui_ImplRoblox.SetRenderRate(0)
+local io = ImGui.GetIO()
+local frame, h = 0, 0
+local function mix(v) h = (h * 31 + math.floor(v * 64 + 0.5)) % 2147483647 end
+game:GetService("RunService").Stepped:Connect(function()
+    frame += 1
+    G.ImGui_ImplRoblox.NewFrame()
+    io.DeltaTime = 1 / 60
+    io:AddMousePosEvent(100 + (frame * 37) % 500, 60 + (frame * 53) % 600)
+    if frame % 7 == 0 then io:AddMouseButtonEvent(0, frame % 14 == 0) end
+    if frame % 11 == 0 then io:AddMouseWheelEvent(0, -1) end
+    ImGui.NewFrame()
+    ImGui.ShowDemoWindow(true)
+    ImGui.Render()
+    for _, dl in ImGui.GetDrawData().CmdLists:iter() do
+        local vd, id = dl.VtxBuffer.Data, dl.IdxBuffer.Data
+        for i = 1, dl.VtxBuffer.Size do local v = vd[i]; mix(v[1].x); mix(v[1].y); mix(v[2].x * 4096); mix(v[2].y * 4096); mix(v[3] / 64) end
+        for i = 1, dl.IdxBuffer.Size do mix(id[i]) end
+        for _, c in dl.CmdBuffer:iter() do mix(c.ClipRect.x); mix(c.ClipRect.y); mix(c.ClipRect.z); mix(c.ClipRect.w); mix(c.ElemCount) end
+    end
+    G.ImGui_ImplRoblox.RenderDrawData(ImGui.GetDrawData())
+    if frame == ARG_FRAMES - 1 then print("DRAWHASH", h) end
+end)