chrono is replaced by jiff

chrono is no longer maintained and replaced by jiff.

chrono is used a couple of times in examples, but the bigger issue is jiff types do not implement Debug. I asked why, but if Debug is not going to be implemented maybe you should implement the way the types should be printed on graphs here.

A bunch of plotters/plotters/src/coord/ranged1d/types/datetime.rs needs to be changed.