Add websocket.handler.before/after/exception signals

[Tronic]

Adding ability to implement middleware functionality on WebSocket handlers by signals that receive websocket parameter.

The flow is:

http.handler.before (request) -> websocket.handler.before (request, websocket) -> handler
 ____________________________________________________________________________________/
|
| -> clean exit: websocket.handler.after (request, websocket)
| -> except Exception: websocket.handler.exception (request, websocket, exception)
| -> cancelled/closed: no signal
                             |
                      any of the above -> http.handler.after(request)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (45e1fc8) 88.306% compared to head (50cec6b) 88.452%.

❗ Current head 50cec6b differs from pull request most recent head 469803d. Consider uploading reports for the commit 469803d to get more accurate results

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2841       +/-   ##
=============================================
+ Coverage   88.306%   88.452%   +0.146%     
=============================================
  Files           92        92               
  Lines         7158      7162        +4     
  Branches      1229      1228        -1     
=============================================
+ Hits          6321      6335       +14     
+ Misses         582       573        -9     
+ Partials       255       254        -1     

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[Tronic]

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