Introduce Async publish and Async/Sync subscription

[adamhathcock]

A lot of things are actually async as well as thread switching is async regardless of source being async or sync. This also matches async by default.

Besides Rhino and Tekla, some apps are using async void for event handing which isn't be a thing.

Requires #417

[codecov]

Codecov Report

Attention: Patch coverage is 73.75415% with 79 lines in your changes missing coverage. Please review.

Project coverage is 13.73%. Comparing base (e9f13e2) to head (e75e5e0).

Files with missing lines	Patch %	Lines
...I3/Speckle.Connectors.DUI/Eventing/SpeckleEvent.cs	26.08%	32 Missing and 2 partials ⚠️
...I3/Speckle.Connectors.DUI/ContainerRegistration.cs	0.00%	11 Missing ⚠️
...le.Connectors.DUI/Eventing/OneTimeThreadedEvent.cs	66.66%	6 Missing and 2 partials ⚠️
...e.Connectors.DUI/Eventing/EventSubscriptionSync.cs	68.42%	5 Missing and 1 partial ⚠️
DUI3/Speckle.Connectors.DUI/Eventing/EventBase.cs	76.19%	5 Missing ⚠️
....Connectors.DUI/Eventing/EventSubscriptionAsync.cs	73.68%	5 Missing ⚠️
...Connectors.DUI/Eventing/WorkerEventSubscription.cs	0.00%	4 Missing ⚠️
...ectors.DUI/Eventing/MainThreadEventSubscription.cs	0.00%	3 Missing ⚠️
...UI3/Speckle.Connectors.DUI/Bridge/BrowserBridge.cs	0.00%	2 Missing ⚠️
...peckle.Connectors.DUI/Models/DocumentModelStore.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           event-aggregator     #505      +/-   ##
====================================================
+ Coverage              8.81%   13.73%   +4.91%     
====================================================
  Files                   240      242       +2     
  Lines                  4526     4682     +156     
  Branches                587      575      -12     
====================================================
+ Hits                    399      643     +244     
+ Misses                 4111     4011     -100     
- Partials                 16       28      +12     

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[JR-Morgan]

Some of the overrides do not use the TopLevelException Handler

We were seeing a crash in Rhino on a OneTimeEventSubscriptionSync subscribe block

[JR-Morgan]

Rhino Document switch events are not clearing the UI.
@adamhathcock mentioned this regression may be existing already on dev.
I think it would be good to investigate, since we did at one point have this down.