Add "fast" option to pericenter/apocenter and support multiple orbits

[adrn]

Right now, .pericenter() and .apocenter() are slow because they do interpolation to figure out a precise value. There should be a fast=True option that skips the interpolation.

We also need to support these methods for multiple orbits in the same object.

[pkaf]

Is looping over the tracers the current preferred way to calculate .apocenter() etc? Just making sure before burning cpus. :)

[adrn]

Yes, but knowing that someone else is feeling that pain will motivate me to actually fix this :)

[pkaf]

I will then add that the pain of not having this feature is ever increasing and will be more so post DR2. Also, it will be useful to have method zmax (maximum vertical height ).

[adrn]

Finally addressed this in #105! Just in time for Gaia :)

[adrn]

Once I get the tests to pass with that PR, I'll merge and release a new version.