Fiber scheduler changes

[samuel-williams-shopify]

In Ruby 3.5/4.0 there are some changes to the fiber scheduler which you should consider adopting.

• Fiber::Scheduler#fiber_interrupt as described https://bugs.ruby-lang.org/issues/21166
• Fiber::Scheduler#blocking_operation_wait is an experimental support for offloading rb_nogvl work to a background thread pool (to prevent stalling the event loop).

Would be interested to see how you'd integrate that with Itsi.

[wouterken]

Thank you for the pointer! I've added a task to build the latest Ruby 3.5 and experiment with those hooks (and also to take a closer look at what you're doing with these inside Async, for inspiration 🙂 )