Fix port selection

[blink1073]

Fixes #1170, by using the same bind_sockets function as is later used to start the http server.

[blink1073]

@kevin-bates should we do something similar in jupyter_client?

[blink1073]

The tornado util function appears to be more robust.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03 🎉

Comparison is base (b5a6306) 79.08% compared to head (6335a8f) 79.12%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1229      +/-   ##
==========================================
+ Coverage   79.08%   79.12%   +0.03%     
==========================================
  Files          68       68              
  Lines        8253     8252       -1     
  Branches     1603     1599       -4     
==========================================
+ Hits         6527     6529       +2     
+ Misses       1301     1299       -2     
+ Partials      425      424       -1     

Impacted Files	Coverage Δ
jupyter_server/serverapp.py	72.76% <100.00%> (+0.06%)	⬆️
jupyter_server/services/contents/filemanager.py	76.31% <0.00%> (-0.62%)	⬇️
...ter_server/services/kernels/connection/channels.py	61.72% <0.00%> (+1.32%)	⬆️

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[kevin-bates]

@kevin-bates should we do something similar in jupyter_client?

I think this makes sense. Are we confident the SO_LINGER portion is unnecessary? This also more closely binds us (pun intended) to tornado - although its exclusion would likely occur in an entirely different code base - but wanted to mention that as a possible deterrent.

[blink1073]

Yeah, I don't think we need LINGER because we aren't actually sending any messages on this socket. We could always inline the method with attribution if we ever decide to move off of tornado.

[blink1073]

Actually, I don't think we need this logic in client, since we're asking the OS to give us a port, not attempting to use a specific one.