[fix] Fix missing LLM I/O content capture in AgentScope

[sipercai]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Reproduction Steps

1. Install dependencies: pip install -r tests/requirements.latest.txt
2. Set up API key for DashScope (or use VCR cassettes)
3. Run tests: pytest tests/test_span_content.py -v

• Test A

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• [] Documentation has been updated