fix a bug happening during sending of super_stream with routing_key

[DanielePalaia]

There is a bug in the routing_key mode of super_stream.

The cache for routes is not general but specific for a routing_key so it needs to be checked for every routing_key.

This PR should solve the issue.

It also adds an example for super_stream with routing_key mode.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.70%. Comparing base (70e9844) to head (8b52d6d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #243      +/-   ##
==========================================
+ Coverage   89.37%   89.70%   +0.32%     
==========================================
  Files          78       78              
  Lines        6741     6742       +1     
==========================================
+ Hits         6025     6048      +23     
+ Misses        716      694      -22     

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