Mark as ractor-safe

[mohamedhafez]

Closes #318

Types of Changes

• Performance improvement when using nio4r in Ractor, and also for when TruffleRuby can run rb_ext_ractor_safe C-extensions in parallel.

Contribution

• I tested my changes locally.
  On MacOS 15.0,
  uname -a: Darwin mohameds-mbp.lan 24.0.0 Darwin Kernel Version 24.0.0: Mon Aug 12 20:51:54 PDT 2024; root:xnu-11215.1.10~2/RELEASE_ARM64_T6000 arm64
  Ruby versions: 3.1.6 and 3.3.5
  Results: 112 examples, 0 failures, 2 pending
• I agree to the Developer's Certificate of Origin 1.1.

STILL REQUIRED:

• someone with more comfort with C-extensions to review if any global state is used and if the extension really is already fully Ractor-safe
• Possibly add tests for changes? Might be hard to test for concurrency issues

[mohamedhafez]

@ioquatix I'm guessing the failing Mac tests just weren't set up to run correctly? Running the test suite on my MacOS 15.0 with both ruby 3.1.6 and 3.3.5, tests seem to pass without issue

[ioquatix]

Yes, the CI will need to be updated, do you want to have a go at making a separate PR to update CI? We can rebase this PR on top of it.

[ioquatix]

AFAIK this gem does not have any thread unsafe state. However, I'll review it before making the next release.

[ioquatix]

Thanks for your contribution.