Add smoothing based on Chebyshev polynomials of the fourth kind

[MalachiTimothyPhillips]

Closes #862

Variant 2: Standard, 1st Kind Chebyshev smoothing with $D^{-1}A$. No restriction on the Chebyshev order.

Variant 3: 4th Kind Chebyshev smoother with $D^{-1}A$. No restriction on the Chebyshev order.

Variant 4: Optimized 4th Kind Chebyshev smoother with $D^{-1}A$. Chebyshev order must be in [1,16] due to needing to compute the $\beta_k$ coefficients.

Variants 3-4 are from https://arxiv.org/pdf/2202.08830.pdf.

These correspond to relaxation type 16.

In addition, relaxation type 19 has been implemented as a "no-op" smoother. This can be used in the case a user wishes to omit the post smoothing step, for example.

p.s.: I'm happy to walk through these changes "offline" on a zoom call.