Fix observationConvention propagation to child chains (#5882)

[redinside-dev]

Summary

Fixes #5882 - The Advisor executed after ToolCallAdvisor lacks the custom observation convention about 'spring.ai.advisor' span.

Problem

In DefaultAroundAdvisorChain.copyAdvisorsAfter(), when creating child chains for advisors that come after a certain advisor, the observationConvention from the parent chain was not being passed to the child chain builder. This caused subsequent advisors in the chain to lose the custom observation convention.

Solution

Pass this.observationConvention to the builder in copyAdvisorsAfter():

return DefaultAroundAdvisorChain.builder(this.getObservationRegistry())
    .observationConvention(this.observationConvention)  // <-- Added this line
    .pushAll(remainingStreamAdvisors)
    .build();

Changes

1. DefaultAroundAdvisorChain.java: Added .observationConvention(this.observationConvention) to the builder chain in copyAdvisorsAfter()
2. DefaultAroundAdvisorChainTests.java: Added 3 tests to verify observation convention preservation:
   • whenCopyingChainWithCustomObservationConventionThenConventionIsPreserved
   • whenCopyingChainWithDefaultObservationConventionThenDefaultIsPreserved
   • whenCopyingStreamChainThenObservationConventionIsPreserved

Testing

All existing tests pass, plus the 3 new tests verify the fix.