Add more kernels #316

This mostly comes from searching around for kernels to test on #279. The citations are probably not the best, but just to have something to point to.

• Rotne–Prager–Yamakawa kernel: https://doi.org/10.1016/j.jcp.2012.09.021.
• Odd-viscosity Stokes kernel: https://doi.org/10.1103/PhysRevFluids.2.094101 and https://doi.org/10.1017/jfm.2021.1079.
• Regularized Stokeslet: https://doi.org/10.1016/j.jfluidstructs.2016.07.006
  • This may not be appropriate for sumpy, since it's not really a fundamental solution.
• Electromagnetic dyadic: https://doi.org/10.1109/8.633855
• Your Favourite Missing Kernel Here.

xref: #315