Allow proc default values that depend on other values

[pedrocarmona]

Add ability to set default values that depend on other values from a given record.

Example:
If slice belongs to cake with frostings, then allow to set frostings in cake slice by default.

class Slice < Sequel::Model
   many_to_one :cake
   plugin :defaults_setter
   
   def self.default_values
      {
        frosting: lambda { |slice| slice.cake&.frosting? },
      }
   end
 end

Cake.create(frosting: true)
Slice.new(cake_id: cake.id).frosting # => true

[jeremyevans]

Thanks for the patch! I'll test and merge later today.

[pedrocarmona]

Thank you Jeremy 🙌