perf: optimize mapped, add benches

benchmarks/propagate.luau

@@ -0,0 +1,27 @@
+local Charm = require("@pkgs/charm/src/lib")
+local bench = require("./bench")
+
+local atom = Charm.atom
+local computed = Charm.computed
+local effect = Charm.effect
+
+for _, w in { 1, 10, 100 } do
+	for _, h in { 1, 10, 100 } do
+		bench.run(`propagate {w}*{h}`, function()
+			local src = atom(1)
+			for _ = 1, w do
+				local last = src
+				for _ = 1, h do
+					local prev = last
+					last = computed(function()
+						return prev() + 1
+					end)
+				end
+				effect(function()
+					last()
+				end)
+			end
+			src(src() + 1)
+		end)
+	end
+end