New cop for extracting complex callbacks code into separate methods

[fatkodima]

When the model have some callback code defined inline via a proc, you need to read the actual code to understand what it does.
This can not be a problem of course for simple one-liners, but for other cases it is better when it is given an explicit name.

# bad
class User < ApplicationRecord
  before_validation do
    foo
    bar
    ...
    baz
  end
end

# good
class User < ApplicationRecord
  before_validation :do_something

  private
    def do_something
      foo
      bar
      ...
      baz
    end
end

# ok
class User < ApplicationRecord
  before_validation -> { do_something }
end

The same applies to controllers/jobs/mailers callbacks.