support proper 32-byte RNG seeds (!126)

- add optional `$.help` to argument `err` of `error throw`
- parse `prng_seed: [u8; 32]` in `rng` and `inbreeding`
- compute the "_local_" seed by hashing the "_global_" seed, the strategy and the iteration index
- pass `--prng-seed: string`, a 64-char long seed to `inbreeding run`