Add todoapp benchmark

bench/implementations/nim-karax-comp-local/examples/scrollapp/scrollapp.html

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+<!DOCTYPE html>
+
+<html>
+<head>
+  <title>Todo app</title>
+</head>
+
+<body id="body">
+
+<div id="ROOT" />
+
+<script type="text/javascript" src="nimcache/scrollapp.js"></script>
+
+</body>
+</html>

bench/implementations/nim-karax-comp-local/examples/scrollapp/scrollapp.nim

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+## Example that shows how to accomplish an "infinitely scrolling" app.
+
+include karaxprelude
+import jstrutils, dom
+
+var entries: seq[cstring] = @[]
+for i in 1..500:
+  entries.add(cstring("Entry ") & &i)
+
+proc scrollEvent(ev: Event; n: VNode) =
+  let d = n.dom
+  if d != nil and inViewport(d.lastChild):
+    # "load" more data:
+    for i in 1..50:
+      entries.add(cstring("Loaded Entry ") & &i)
+
+proc createDom(): VNode =
+  result = buildHtml():
+    tdiv(onscroll=scrollEvent, style="height: 400px; overflow: scroll"):
+      for x in entries:
+        tdiv:
+          text x
+
+setRenderer createDom

bench/implementations/nim-karax-comp-local/examples/scrollapp/scrollapp.nims

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+--path: "../../src"