Potential race condition caching the value of PortName when subscribing to Device node

[glopesdev]

@aspaNeuro reported a potential race condition when concurrently initializing multiple Device nodes inside a loop where PortName may be cached too late, leading to name clashes during initialization.

If confirmed, this could potentially be traced back to the assignment below which is executed inside an async method. Because we do not control which parts of async methods run synchronously vs not, we may have to move this caching earlier to ensure it is made synchronous with either subscription or observable construction.

harp/Bonsai.Harp/Device.cs

Line 322 in eae1176

var portName = PortName;