feat: refine implicit association syntax to declare traits without factory keyword

[vburzynski]

This refines the implicit association syntax to make it possible to declare traits without having to use the special factory keyword.

previously you would have to write:

factory :comment do
  user factory: [:user, :admin], name: "Joe Slick"
end

which can now be simplified as:

factory :comment do
  user :admin, name: "Joe Slick"
end

this mirrors how you would write this in the explicit syntax:

factory :comment do
  association :user, :admin, name: "Joe Slick"
end

I was inspired after looking at #1552 which, as of this writing, has been open since 2022.