Add an ability to import two containers in the same class/module

[woarewe]

Currently, if we try to do something like this:

A = F::Container.new.tap do |container|
  F::Container::Define.build(container: container).instance_exec do
    namespace :math do
      f(:value) { "A" }
    end
  end
end

B = F::Container.new.tap do |container|
  F::Container::Define.build(container: container).instance_exec do
    namespace :math do
      f(:value) { "B" }
    end
  end
end

class Service
  include A.import
  include B.import

  def call
    f("math.value")
  end
end

puts Service.new.() # => 'B'

Basically, if you try to import several containers the last one overrides all the previous ones.
But instead, we should make it work according to the following specification

Importing a container

We need to add a mechanism to store the imported containers in a box with assigned labels.
The first imported container gets the label main. Basically, the target class or a module should have a storage, like a hash, with labels as keys and with containers as values.

For example:

class Service
  include A.import # this line should store { main: A }
  
  def call
    f('math.value') # => should work
    f('main.math.value') # should also work
  end
end

If one container is imported

• The behavior stays the same

** If several containers are imported

• An attempt to import a second module without an explicit alias should raise an error

  class Service
  include A.import # this line should store { main: A }
  include B.import # this line should fail
  include B.import.as(:second) # ok will work
end

• The function f should look through the containers from top to bottom if there is no top namespace provided.