Update partitioning the raw tree (means converting it to "non-raw" tree)

Finally achieves to pass the first internaltree test.

lib/outlook/internal_tree.ex

@@ -24,6 +24,6 @@ defmodule Outlook.InternalTree do
     # validate_sibling_collocation(tree)
     tree
     |> RawInternalBasic.set_split_markers()
-    |> RawInternalBasic.partition_textnodes()
+    |> RawInternalBasic.partition_to_tunits()
   end
 end