fix(core): measure the impact of the faster type checks for dtype=object
fix(core): measure the impact of the faster type checks for dtype=object

Before: it took 0:02:43.718827 to convert 12,748,986 rows (1.8 Gb), which is 77,871 rows per second
After: it took 0:00:07.244279 to convert 12,748,986 rows (1.8 Gb), which is 1,759,869 rows per second

maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex