v0.4.3: Improvements to (Gaia) cluster simulation

A couple of improvements were made to cluster simulation:

• ocelot.model.observation.BaseObservation now has two additional default methods for applying photometric and astrometric errors. These can be overwritten for observation types that require additional functionality beyond simple Gaussian errors.
• The GaiaDR3ObservationModel class now uses this photometric data overwrite to model underestimated BP and RP fluxes in Gaia DR3, slightly improving the realism of cluster CMDs further.