T1: Use FFT to encode polynomials in evaluation form

[ggutoski]

Build a quick-and-dirty prototype for namespace support in VID by using our existing KZG implementation + a bunch of FFTs. A proper solution is #339 , but that will take time. Best to get a prototype working soon.

Limitations of the quick-and-dirty prototype that would be solved by #339 :

1. Slower. So many FFTs.
2. Payload recovery is possible only if the polynomial degree (plus 1) is a power of 2.

Any PR closing this issue should include tests that demo the ability to make KZG proofs for individual field elements in the payload, checkable against the payload commitment.