Change the scaling behavior to default to representing servings rather than a multiplier

[melaniejones731]

The documentation for the CLI says that scale is implemented like this:

Scaling Recipes
Scale recipes on the fly using the : notation or the --scale flag:

# Double a recipe
cook recipe "Pizza.cook:2"

# Scale to 1.5x
cook recipe "Cake.cook" --scale 1.5

# Quarter a recipe
cook recipe "Soup.cook:0.25"

This is multiplier behavior.

I don't believe this is intuitive, especially when recipes servings are larger. If I am cooking a recipe with serving size 20, it is more likely that I want to serve 6 or 24 people than 10 or 40.

To me, it is vastly more conceivable to think if a user inputs cook recipe "Pizza.cook:2", their intent is to scale the recipe to 2 SERVINGS.

I would like to modify the default behavior to this:

Scaling Recipes
Scale recipes on the fly using the : notation or the --scale flag:

# Double a recipe
cook recipe "Pizza.cook:2x"

# Scale to 1.5x
cook recipe "Cake.cook" --scale 1.5

# Quarter a recipe
cook recipe "Soup.cook:0.25x"

# Scale to serving 2 people
cook recipe "Pizza.cook:2" 

# Scale to serving 10 people
cook recipe "Pizza.cook:10"

However, doing so could be a breaking change unless the underlying code in scale.rs for scale_to_target is updated to gracefully handle the scenario "unit" is none and serving is defined (or not) as it could lead to ambiguity when cli calls are made.