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/color.nu

@@ -84,13 +84,13 @@ def try-string-to-int []: string -> int {
 
 export def "color from-string" [s: string]: nothing -> record<r: float, g: float, b: float> {
     let res = $s
-        | parse --regex '^0x(?<r>..)(?<g>..)(?<b>..)$'
+        | parse --regex '^#(?<r>..)(?<g>..)(?<b>..)$'
         | into record
 
     if $res == {} {
         error throw {
             err: "invalid HEX color format",
-            label: $"format should be '0xRRGGBB', found ($s)",
+            label: $"format should be '#RRGGBB', found ($s)",
             span: (metadata $s).span,
         }
     }