Add Ruby 3.0 and 3.1 to CI, Split out Faraday 1 and 2

[petergoldstein]

This PR adds Ruby 3.0 and 3.1 to the CI matrix and adds a new row for Faraday major version (given the recent release of Faraday 2 and the middleware specific changes)

To support this goal this PR also:

1. Addresses a few lints raised by Rubocop
2. Moves a number of development dependencies from the Gemfile to the gemspec
3. Adds dedicated Faraday 1 and Faraday 2 gemfiles
4. Sets a minimum Ruby version of 2.5
5. Fixes an ActiveSupport loading issue for recent versions of ActiveSupport

Everything runs green on my fork.

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[nanego]

Thank you for this Pull Request. The current version of the gem seems to be incompatible with Faraday 2.
I had to add this line to my Gemfile to prevent any update to Faraday 2:
gem 'faraday', '~> 1.0'