Add docstring for SocketStream.send_all

[Madhur-7568]

Summary

Adds a docstring to SocketStream.send_all so it is included in the public API documentation and satisfies the type completeness check.

Testing

• python -c "from trio import SocketStream; print(SocketStream.send_all.doc)"
• python src/trio/_tests/check_type_completeness.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (0db3cf4) to head (69167e8).

Additional details and impacted files

@@                 Coverage Diff                  @@
##                main        #3458         +/-   ##
====================================================
+ Coverage   99.98455%   100.00000%   +0.01545%     
====================================================
  Files            128          128                 
  Lines          19417        19417                 
  Branches        1317         1317                 
====================================================
+ Hits           19414        19417          +3     
+ Misses             1            0          -1     
+ Partials           2            0          -2     

Files with missing lines	Coverage Δ
src/trio/_highlevel_socket.py	100.00000% <ø> (ø)

... and 1 file with indirect coverage changes

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[A5rocks]

Please just remove the Sphinx directive that is causing this to be documented.

Also please don't respond with an LLM-generated response.

[Madhur-7568]

thanks for the clarification. I will remove the sphinx directive and update the pr.