T2: VID hello-world namespace support

[ggutoski]

Make a feature-complete (but rudimentary) implementation of VID namespace support for ADVZ scheme.

Goals

• Get an API we can use downstream. We will need to iterate on this API.
• Get something working. It'll be slow at first. After we have feature-completeness we can pick some low-hanging optimization fruit such as [low priority] Univariate KZG in evaluation form #339 Univariate KZG multiproofs (in eval form) #387 .