perf(TailwindStyle): skip redundant traversal and avoid unnecessary r…

[HugoHSun]

…ecompiles

🎫 Resolve RM-15353

🎯 What does this PR do?

• when the added node is itself a TailwindRoot, traverse() already recurses
  into its descendants — no need to also querySelectorAll into it. moved that
  check into an else branch
• also replaced unconditional shouldUpdate = true with a classesSet size check
  in both branches, so setClasses only fires when new classes were actually found
• adds back fix(TailwindStyle): detect nested TailwindRoot elements on DOM updates #1404 and the overlap test case suggested in the review

🧪 QA tips

• no regression of tailwind style not applying in PJAX navigation

📸 Screenshot or Loom

[HugoHSun]

@rafegoldberg the changes are all good to go!