Update scan benchmarks to have a range of 16K-128K iterations. As of...

Update scan benchmarks to have a range of 16K-128K iterations. As of https://github.com/tensorflow/tensorflow/commit/5802096c267c805f6a69798aac10aefef759bb9f, TensorFlow Eager no longer exhibits quadratic behavior. The benchmark is still ~5x slower in eager mode vs. graph mode, and maybe slightly worse than linear:

n     Graph Time (s)  Eager Time (s)      Ratio
-----------------------------------------------
 16K            0.35             1.8        5.1
 32K            0.64             3.6        5.6
 64K            1.1              7.2        6.5
128K            2.4             14.8        6.2

PiperOrigin-RevId: 197505257