fix: streaming error handling type mismatch

[finbarr]

Summary

This PR fixes a type mismatch error that occurs when handling errors during streaming responses. The streaming error handlers were passing plain hashes to ErrorMiddleware.parse_error, but parse_error expected Faraday response objects with a body method.

Problem

When errors occurred during streaming, the application would crash with:

NoMethodError: undefined method 'body' for an instance of Hash

Solution

• Created an ErrorResponse struct that mimics the Faraday::Response interface
• Updated all streaming error handlers (handle_error_chunk, handle_failed_response, handle_error_event) to use a new create_error_response helper method
• Added nil-safe handling for the env parameter in streaming contexts
• Added comprehensive tests to verify the fix

Testing

Added tests to spec/ruby_llm/error_handling_spec.rb that verify:

• Error chunks are handled correctly with both nil and populated env parameters
• Failed responses are processed properly
• The ErrorResponse struct provides the expected interface

All tests pass and the streaming error handling now works consistently with regular response error handling.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.00%. Comparing base (a9a1446) to head (34657a1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/ruby_llm/streaming.rb	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #292      +/-   ##
==========================================
+ Coverage   86.64%   87.00%   +0.36%     
==========================================
  Files          79       79              
  Lines        3129     3133       +4     
  Branches      613      614       +1     
==========================================
+ Hits         2711     2726      +15     
+ Misses        418      407      -11     

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[crmne]

Thanks for your work on this! We ended up going with #273 which has been merged. The streaming error handling issue is now resolved.