Add as development dependencies gems extracted from Ruby stdlib

[davidrunger]

Specs are currently failing on master on my local machine when I try to run specs with BUNDLE_GEMFILE=/home/david/code/paper_trail/gemfiles/rails_6.1.gemfile bundle exec rspec. This isn't yet reflected in any CI builds on master, but I believe that it would be, if a build were to be triggered on master. The same error is also occurring in recent PRs that have been put up (e.g. this PR with this failed build and this PR with this failed build).

I'm not sure why these errors have started occurring now, without any changes in master since the last commit on master that passed all checks. Maybe bundler changed its behavior, and we are pulling in a new/recent version of bundler with some relevant behavior change?

But, anyway, the errors seem to be caused by the extraction of various gems from the Ruby standard library into standalone gems, specifically:

1. bigdecimal
2. drb
3. mutex_m

This change adds those gems as development dependencies of paper_trail.

Although they are not yet causing errors, the following gems were causing a warning for me when I ran specs using Ruby 3.4.2 with BUNDLE_GEMFILE=/home/david/code/paper_trail/gemfiles/rails_6.1.gemfile bundle exec rspec:

1. benchmark
2. logger

These are the warnings:

/home/david/code/paper_trail/spec/spec_helper.rb:64: warning: logger was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add logger to your Gemfile or gemspec to silence this warning.
/home/david/.rbenv/versions/3.4.2/lib/ruby/gems/3.4.0/gems/activesupport-6.1.7.10/lib/active_support/dependencies.rb:299: warning: benchmark was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add benchmark to your Gemfile or gemspec to silence this warning.
Also please contact the author of activesupport-6.1.7.10 to request adding benchmark into its gemspec.

To avoid these warnings, I am also adding these two gems as development dependencies.

Additionally, this change adds a require "logger" statement to spec/spec_helper.rb. This isn't needed for the other gems (I'm guessing because activerecord and/or actionpack have require statements for benchmark, bigdecimal, drb, mutex_m?), but it seems to be needed for logger; without it, we get an error when trying to boot specs about NameError: uninitialized constant ActiveSupport::LoggerThreadSafeLevel::Logger.

I think that these changes will get specs passing on master again.

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Thank you for your contribution!

Check the following boxes:

• Wrote good commit messages.
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests. N/A: I believe that tests will fail right now if run on master. If tests pass on this branch, that is an indication of success; I don't think that new tests are warranted.
• Added an entry to the Changelog if the new code introduces user-observable changes. N/A: This isn't a user-observable change.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.

[davidrunger]

I'm not sure of the best way to determine which version specifiers to write here.

For each gem, I looked at the latest version available (at rubygems.org).

If the latest version has a major version of 0, then I did ~> <latest version>.

If the latest version has a non-zero major version, then I did ~> <major.minor of latest version>.

I have little idea if this is an optimal algorithm, and would be happy to make any changes.

[modosc]

this seems ok to me.

going forward we might want to drop unsupported rails versions from the test matrix. per this doc 6.1 was dropped on October 1, 2024 (and 7.0 will be dropped tomorrow!).