fix: improve experiments helpers tags

• Include helpers into both type:experiment and experiment tags
• Run clean-ups in both cases as well

This way, it's possible to avoid adding :experiment tag to experiment unit tests:

    # file: spec/other_experiments/my_experiment_spec.rb
    RSpec.describe MyExperiment, type: :experiment do
      # works as expected
    end

    # file: spec/experiments/my_experiment_spec.rb
    RSpec.describe MyExperiment do
      # works as expected
    end

    # file: spec/request/login_spec.rb
    RSpec.describe "Login" do
      describe "sign in flow", :experiment do
        # experiment heleprs available here too
      end
    end

And it's possible to run specs for given tags:

rspec --tag experiment      # run all examples with `:experiment` tag
rspec --tag type:experiment # run experiment unit tests

See-Also: !172 (merged)