TangoMonitor: Improve error message in case of timeout.

Adds information about the monitor and threads involved when TangoMonitor::get_monitor times out.

I used the thread's omnithread id to identify them. I don't know if this is particularly meaningful for the user but hopefully it is better than nothing. I couldn't work out if there is any way we can add a meaningful name to each thread as some of them are started by omniORB.

I also went through and made sure that every TangoMonitor has a unique name. This involved refactoring DeviceImpl::DeviceImpl to use a std::string_view so I didn't have to repeat myself.

Blocked by !1199 (merged) as I have added a Catch2 test for this.

Closes #984.