Add more precise typing to transformation functions

[majosm]

Changes transformation functions to return as specific a type as possible. This helps avoid having to add casts in code that calls these functions, e.g.:

dag = cast("DictOfNamedArrays", pt.tag_all_calls_to_be_inlined(dag))
dag = cast("DictOfNamedArrarys", pt.inline_calls(dag))

becomes

dag = pt.tag_all_calls_to_be_inlined(dag)
dag = pt.inline_calls(dag)