Mark arguments in callbacks traces

We need to have better visual split between arguments of callback trace body like this:

For `update` trace
```elixir
arg 1 (assigns): %{new_assign: "activity-log"}

arg 2 (socket): %Socket{...}
```

For `handle_event` trace
```elixir
arg 1 (event): "increment"

arg 2 (params): %{"value" => 1}

arg 3 (socket):  %Socket{...}
```