v2.5.5 fixes Modbus teardown and missing events with async tag creation

Thanks to user @nc-koko for surfacing these problems.

• Events were being missed on tag creation when using asynchronous mode. Specifically the created event was missing.
• Shutdown was not fully cleaning up internal library Modbus resources in some circumstances under Windows.
• Thanks to @timyhac for experimenting on the shutdown problem. I think we might still have some work to do there with the combination of the core library, Windows and .Net, but it is a lot better.

Please double check that you are getting all the events you think you should get after upgrading. And, please let me know if you see duplicate events! I did not see any in my testing, but absence of evidence is not evidence of absence.