Fix speed regression due to PySequence_Fast in for loop.
Fix speed regression due to PySequence_Fast in for loop.

PySequence_Fast isn't so fast after all (due to multiple branching),
was a 35% slowdown for looping over lists. Now it handles tuples as
well with only about a 4% slowdown to lists compared to before.

bhy/cython-haoyu,bhy/cython-haoyu,bhy/cython-haoyu,bhy/cython-haoyu