Local support size in singular integrals

[unalmis]

In #1546 we change default parameters that determine the partition size of the support for the singular integrals to account for grid anisotropy. Basically, this makes the partition region closer to a circle in real space, matching the symmetry of the singularity e.g. $(x-x')^{-n}$, with the goal of more robust convergence across wider aspect ratio range. This issue is to add an option to account for the local grid anisotropy which might improve convergence for more strongly shaped geometry. Would just need to update the st and sz params in the interpolators to one-dimensional arrays, then run the convergence testing script on pull request #1546.