effects: Add support for :type as standalone, unnamed types. ( :float -- ) pprints...

effects: Add support for :type as standalone, unnamed types. ( :float -- ) pprints as ( _: float -- ), and ( :( a -- b ) -- ) works, etc. :union{ foo bar } pprints as object but could be improved if the effects parser uses the prettyprinter somehow.
Move ?execute-parsing to parser to avoid circularity.