Make the const generic degree into a generic trait struct

[teor2345]

This PR depends on #65.

It is an extremely large change, so it would help to get it merged within a day or two. Otherwise it will conflict with other PRs. It is not easy to re-do, due to the number of manual fixes required.

This PR replaces the MAX_POLY_DEGREE const generic with a PolyConf trait containing a MAX_POLY_DEGREE constant.

It also makes a bunch of associated fixes and replacements:

• FULL_RES_POLY_DEGREE becomes TestRes
• IRIS_BIT_LENGTH becomes IrisBits
• There are new FullRes and TinyTest config types, which are currently only used in tests
• Some automatic derives can't be used, and need to be re-implemented manually
• Some code is cleaned up to make this change simpler

The mass replaces follow these instructions: https://github.com/ZcashFoundation/zebra/blob/main/book/src/dev/mass-renames.md#universal-renames-with-sed

This is part of #59, but I'm going to replace Coeff in another PR.

[teor2345]

Rebased to resolve merge conflicts, now I'm going to merge with Eduardo's previous approval.