Action & Channel should be modules

[vladfaust]

Composition over inheritance!

Ideal code would be:

struct MyAction
  include Prism::Action
  include Prism::Params
  include Prism::Auth
  
  auth!

  params do
    param :foo, Int32
  end
  
  def call
    # ...
  end
end

That said, following must be implemented:

• Prism::Action includes Callbacks and they do actually work (see Can't call re-defined method. crystal-lang/crystal#1104 (comment))
• MyAction can be an abstract struct and callbacks should work in this case as well
• Prism::Params and Prism::Auth included along with Prism::Action automatically inject those before callbacks Introduce Prism::Action::Params & Prism::Action::Auth, which is more straightforward IMO