Add ActiveSupport 7.1 as default setup

[tomascco]

I made this PR based on #314, so:

• Updated the "main" Gemfile to Rails 7.1
• Moved the old Gemfile to the gemfiles folder
• Updated all Gemfiles

I ran rake spec with all Gemfiles, but got a Deprecation Warning that a didn't succeed in solving:

DEPRECATION WARNING: Support for `config.active_support.cache_format_version = 6.1` has been deprecated and will be removed in Rails 7.2.

(called from <top (required)> at arbre/spec/rails/rails_spec_helper.rb:5)

One solution that I found is to define the config on spec/rails/rails_spec_helper.rb:

# from
Combustion.initialize! :action_controller,
                       :action_view

# to
Combustion.initialize! :action_controller, :action_view do # line 5
  config.active_support.cache_format_version = 7.1
end

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (5f9cc4e) 92.52% compared to head (708df54) 92.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #537 +/- ## ======================================= Coverage 92.52% 92.52% ======================================= Files 17 17 Lines 468 468 ======================================= Hits 433 433 Misses 35 35 ```

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