lepton/cci: run stringer with "go run"

[dolmen]

Run the stringer command (for code generation) using go run instead of go install to avoid affecting the developer's global $GOBIN.

See also #95.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.8%. Comparing base (5bcc204) to head (cc2377d).
Report is 3 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #96   +/-   ##
=====================================
  Coverage   51.8%   51.8%           
=====================================
  Files        102     102           
  Lines      13073   13073           
=====================================
+ Hits        6773    6774    +1     
+ Misses      6008    6007    -1     
  Partials     292     292           

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[maruel]

Thanks!