SpeedscopeFrame: change to class-style namedtuple
SpeedscopeFrame: change to class-style namedtuple

This commit converts SpeedscopeFrame from a non-class-style namedtuple
to a class-style namedtuple for readability.

joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument