write function to do checks on observations and identify if there's a problem with the input astrometry before sending it on the C++ code for fitting

[mschwamb]

We want a function that would look at d structure before observation structure is populated in https://github.com/Smithsonian/layup/blob/97bdfe1ea32e74b726ee5d8ba08f935d2833931f/src/layup/orbitfit.py#L49

the function should return a bool value true if orbitfit should proceed or not actually call the orbitfit a fail and skip sending on to the C++ code and set the success flag to be a failure so the output is all nans in the orbit parameters data structure other than objectID (related to #180)

Conditions when we should not sent on to the C++ orbit fitting code:

• if data["ra'] or data["dec"] is not numeric (aka Nans or nones)
• len of data is less than 3
• data[et] is less than zero
• any of these values data["x"], data["y"], data["z"], data["vx"], data["vy"], data["vz"]

[mschwamb]

proposal we issue flag of -1 if the fit fails because the input is bad (the above conditions cause failures)