Add 'conn_id' field to sync_once span

[erikjohnston]

This is to make it easier to see which sync requests are for which connection when debugging.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.02%. Comparing base (05505a5) to head (ef8e3a7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4290   +/-   ##
=======================================
  Coverage   85.01%   85.02%           
=======================================
  Files         274      274           
  Lines       30043    30043           
=======================================
+ Hits        25542    25543    +1     
+ Misses       4501     4500    -1     

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