Chebyshev revisions

This makes the Chebyshev lab more suitable as a precursor to the labs involving the pseudospectral method for boundary value problems.

- [x] Add an explanation of how the computation of the Chebyshev coefficients uses the IDCT.
- [ ] Use the DST to implement Chebyshev differentiation and integration.

More edits should be made to the Pseudospectral lab so that it actually uses what the do here.
That should be done in a separate PR after this PR and https://github.com/byuimpact/numerical_computing/pull/600 are finished.