Add more websocket connection tests and fix bugs

[blink1073]

This exercise found a few bugs in ZMQChannelsWebsocketConnection.
Also, it seems odd to me that handle_outgoing_message is defined on the abc but isn't used anywhere. Was that an oversight @Zsailer?

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.72%. Comparing base (890b882) to head (58747cc).
Report is 278 commits behind head on main.

Files	Patch %	Lines
...ter_server/services/kernels/connection/channels.py	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1085      +/-   ##
==========================================
- Coverage   77.35%   76.72%   -0.64%     
==========================================
  Files          68       68              
  Lines        8299     8301       +2     
  Branches     1649     1650       +1     
==========================================
- Hits         6420     6369      -51     
- Misses       1462     1501      +39     
- Partials      417      431      +14     

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[Zsailer]

Thanks @blink1073!

Also, it seems odd to me that handle_outgoing_message is defined on the abc but isn't used anywhere. Was that an oversight @Zsailer?

And yes, this was an oversight. I've opened #1089 to fix this.

[Zsailer]

Actually let's merge #1089 first, then rebase this PR to make sure the tests pass okay.

[blink1073]

I'll cut another RC once this is merged.