Add io_close to TestScheduler.

In Ruby 4.1, IO#close without a scheduler io_close hook falls through to
maygvl_close with RB_NOGVL_OFFLOAD_SAFE, which calls
rb_fiber_scheduler_blocking_operation_wait. With a worker-pool scheduler
this causes a fiber switch, and GC compaction can then move the
blocking_operation VALUE — crashing in get_blocking_operation.

Fix: add io_close to TestScheduler delegating to @selector.io_close so
Ruby marks done=1 and skips maygvl_close entirely.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: samuel-williams-shopify

fixtures/io/event/test_scheduler.rb

@@ -114,6 +114,10 @@ def fiber_interrupt(fiber, exception)
 			unblock(nil, FiberInterrupt.new(fiber, exception))
 		end
 
+		def io_close(io)
+			@selector.io_close(io) if @selector.respond_to?(:io_close)
+		end
+		
 		def io_wait(io, events, timeout = nil)
 			fiber = Fiber.current