Improve the pre-computed `root` parameters of polynomial rings

[inbelic]

Cf. Discussion following from https://github.com/google/heir/issues/543#issuecomment-2031067952.

The current pre-computed (prime, 2n-th primitive root) in scripts/generate_static_roots pairs are just a collection of random primes for some default values of n. These could be more applicable to RNS decomposition and could include pairs that are used in various popular schemes, eg. Dilithium, Falcon.