k256+p256+p384: add PrimeField constant tests

[tarcieri]

Adds tests for the TWO_INV, ROOT_OF_UNITY, and ROOT_OF_UNITY_INV constants, based on the tests generated via ff_derive.

Some of them are currently failing and have been annotated with #[ignore] and a TODO comment.

[tarcieri]

Note: they're copy-pasted for now, but once I get these all working (including DELTA) I can extract them into elliptic-curve::dev as a macro or something

[fjarri]

I think there are a few tests missing here:

• MULTIPLICATIVE_GENERATOR ^ ((modulus - 1) >> S) == ROOT_OF_UNITY
• MULTIPLICATIVE_GENERATOR ^ (2^S) == DELTA

[tarcieri]

Yeah as implied in the comment above yours the DELTA constants aren't defined yet

[tarcieri]

Whoa, just hit an ICE on stable Rust (looks like while compiling the dependencies):

https://github.com/RustCrypto/elliptic-curves/actions/runs/4078778175/jobs/7029397528

Edit: filed an issue rust-lang/rust#107613

[tarcieri]

Okay, after an ICE and failures possibly related to GitHub rewriting OS package tarballs I'm going to land this while it's green.

Will backfill a few additional tests and try to consolidate the definitions of the test into a reusable macro.