Caustic

This release performs a major refactor to rename all methods with descriptive names. This includes:

- Greek letters alpha, kappa, psi renamed to deflection_angle, convergence, potential
- deflection_angle made more explicit with reduced_deflection_angle and physical_deflection_angle
- ThickLens lensing made more explicit, base deflection angle calculator is pure raytrace, now physical_deflection_angle throws an error, reduced_deflection_angle throws a warning and points to effective_reduced_deflection_angle
- project moved from src directory to simpler caustic directory
- cosmology made more explicit with dist to distance and Sigma_cr to critical_surface_density
- Pixelated source and lens made more explicit with source now called Pixelated and lens now called PixelatedConvergence leaving open for future work: PixelatedPotential and other variants
- Sersic parameters renamed to match literature with index going to n also now q is a true axis ratio which stretches only the minor axis and not an alternative definition which stretches both axes

A number of development updates have been added:
- No longer reliant on torch interp1d
- Docstrings added for classes and methods
- Added "Simulator" object to simplify the interface
- Adding "Packed" object to identify how parameters are transported through the simulator
- Kappa grid bug fix
- Coverage tests

All model components inherit from a `Parametrized` class, which keeps track of the directed acyclic graph underlying them. This enables passing parameters as args lists, kwargs dictionaries or flatten tensors through arbitrary hierarchical models. It also enables easily setting parameters as static (fixed) or dynamic (sampled and passed into the simulator at runtime).