fix: restore error parameter in SpanTransformer.end()

[dwmkerr]

Summary

• Restore _error parameter in SpanTransformer.end() method
• Add eslint-disable comment to suppress unused var warning
• Fixes build error where claude-code-executor.ts passes error to end()

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.96%. Comparing base (1a02736) to head (f38faba).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
+ Coverage   85.58%   85.96%   +0.37%     
==========================================
  Files           3        3              
  Lines         111      114       +3     
  Branches       54       57       +3     
==========================================
+ Hits           95       98       +3     
  Misses         16       16              

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