Shorthand WebSocketTransport factories with serializers

[yurii-prykhodko-solid]

Adds shorthand constructors to WebSocketTransport classes, so attaching a serializer to one is now a bit simpler.
The user code will be slightly more concise also.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% 🎉

Comparison is base (0019a29) 90.13% compared to head (e1d01ba) 90.15%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
+ Coverage   90.13%   90.15%   +0.02%     
==========================================
  Files          44       44              
  Lines        2819     2825       +6     
==========================================
+ Hits         2541     2547       +6     
  Misses        278      278              

Files Changed	Coverage Δ
...rc/transport/websocket/websocket_transport_io.dart	83.05% <100.00%> (+1.91%)	⬆️

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[KSDaemon]

👍🏻 I think it is a good addition: less boilerplate code and cleaner look :)

[konsultaner]

love it!