feat(fish): add sourceenv script

modules/programs/fish.nix

@@ -61,6 +61,22 @@ in
           functions = {
             fish_greeting = "";
             cheat = "cht.sh $argv | bat -p";
+            sourceenv = ''
+              set -f envfile "$argv"
+              if not test -f "$envfile"
+                echo "Unable to load $envfile"
+                return 1
+              end
+              printf "exported"
+              while read line
+                if not string match -qr '^#|^$' "$line"
+                  set item (string split -m 1 '=' $line)
+                  printf " $item[1]"
+                  set -gx "$item[1]" "$item[2]"
+                end
+              end < "$envfile"
+              printf "\n"
+            '';
           };
         };
       };