Fix timeout events getting lost on Windows

src/crystal/system/event_loop.cr

@@ -11,7 +11,7 @@ abstract class Crystal::EventLoop
   # Creates a timeout_event.
   abstract def create_timeout_event(fiber : Fiber) : Event
 
-  abstract struct Event
+  module Event
     # Frees the event.
     abstract def free : Nil
 

src/crystal/system/unix/event_libevent.cr

@@ -5,7 +5,9 @@ require "./lib_event2"
 {% end %}
 
 # :nodoc:
-struct Crystal::LibEvent::Event < Crystal::EventLoop::Event
+struct Crystal::LibEvent::Event
+  include Crystal::EventLoop::Event
+
   VERSION = String.new(LibEvent2.event_get_version)
 
   def self.callback(&block : Int32, LibEvent2::EventFlags, Void* ->)

src/crystal/system/wasi/event_loop.cr

@@ -33,7 +33,9 @@ class Crystal::Wasi::EventLoop < Crystal::EventLoop
   end
 end
 
-struct Crystal::Wasi::Event < Crystal::EventLoop::Event
+struct Crystal::Wasi::Event
+  include Crystal::EventLoop::Event
+
   def add(timeout : Time::Span?) : Nil
   end
 

src/crystal/system/win32/event_loop_iocp.cr

@@ -88,7 +88,9 @@ class Crystal::Iocp::EventLoop < Crystal::EventLoop
   end
 end
 
-struct Crystal::Iocp::Event < Crystal::EventLoop::Event
+class Crystal::Iocp::Event
+  include Crystal::EventLoop::Event
+
   getter fiber
   getter wake_at
   getter? timeout