Docs: add UDP sockets guide page

[sgerbino]

Adds 4.guide/4q.udp.adoc covering the corosio UDP API: udp protocol tag, open/bind, connectionless and connected modes, message flags, socket options, multicast, cancellation, and a TCP-vs-UDP comparison. Wires the new page into nav.adoc after Unix Domain Sockets.

[cppalliance-bot]

An automated preview of the documentation is available at https://238.corosio.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-04-28 18:13:52 UTC

[cppalliance-bot]

GCOVR code coverage report https://238.corosio.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://238.corosio.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://238.corosio.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-04-28 18:23:35 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.71%. Comparing base (e49d180) to head (bdab9e5).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #238   +/-   ##
========================================
  Coverage    77.71%   77.71%           
========================================
  Files           96       96           
  Lines         7298     7298           
  Branches      1787     1787           
========================================
  Hits          5672     5672           
  Misses        1108     1108           
  Partials       518      518           

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