[PROJECT] Use Choclo in Harmonica forward modelling functions

[santisoler]

Fatiando has a new library called Choclo that is designed to host kernel functions for performing forward modelling functions with different geometries: point masses, dipoles and rectangular prisms. Choclo's forward modelling functions compute the gravity and magnetic fields of a single source on a single computation point.

We would like to refactor the forward modelling functions we have in Harmonica so they can make use of Choclo under the hood. This would simplify Harmonica's code base and reduce its testing suite since we can rely on the (even more) exhaustive tests that Choclo has.

This issue would be an "umbrella issue" for a few others. We would tackle it by solving each one of the smaller ones.

TODO:

• [x] #400
• [ ] #369
• [ ] Warn when computing magnetic fields on singular points of prisms
• [ ] Use Choclo functions for point masses (in Cartesian coordinates)
• [x] #414
• [ ] Use Choclo functions for point masses (in spherical coordinates)
• [ ] Implement magnetic field forward functions for dipoles (in spherical coordinates)

[santisoler]

I ended up disliking these type of "umbrella issues", so I'm closing it in favor of using GitHub Projects instead: https://github.com/orgs/fatiando/projects/2