mix colors for hybrid recoding strategies

• define scripts/color.nu to manipulate RGB colors, especially mix two colors together
• compute the color of hybrid recoding strategies as a weighted sum of the two simple recoding strategies involved, e.g. if the strategy is "10% of the time recode 2 shards and 90% of the time recode 3", then the color of that curve will be 10% the color of the simple strategy recoding 2 shards and 90% the color of the other simple strategy recoding 3 shards
• make the hybrid curves transparent and dashed

example

scripts/inbreeding/plot.nu

@@ -87,7 +87,7 @@ export def main [data: path, --save: path, --options: record<k: int>] {
 
             let alpha = match $it.strategy.type {
                 "single" => 1.0,
-                "double" => 0.5,
+                "double" => 0.3,
             }
 
             { color: $color, line: { alpha: $alpha } }