support proper 32-byte RNG seeds

• 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

bins/inbreeding/run.nu

 use consts.nu
-use ../../.nushell cargo "cargo bin"
 use ../../.nushell error "error throw"
 
 const VALID_HEX_CHARS = "abcdefABCDEF0123456789"
@@ -81,19 +80,6 @@ export def main [
         mkdir $output_dir
         print $"data will be dumped to `($output_dir)`"
 
-        # compute a unique seed for that strategy and global seed
-        let seed = $s + $"($prng_seed)"
-            | hash sha256
-            | split chars
-            | last 2
-            | str join
-            | $"0x($in)"
-            | into int
-        # compute all the seeds for that strategy, one per scenario
-        let seeds = cargo bin rng ...[ -n $options.nb_scenarii --prng-seed $prng_seed ]
-            | lines
-            | into int
-
         for i in 1..$options.nb_scenarii {
             let output = [ $output_dir, $"($i)" ] | path join
 
@@ -108,7 +94,7 @@ export def main [
                 --test-case recoding
                 --strategy $s
                 --environment $options.environment
-                --prng-seed ($seeds | get ($i - 1))
+                --prng-seed ([$prng_seed, $s, $i] | str join | hash sha256)
             ] out> $output
         }