[feat] Add Semantic Scholar tools

[danialza]

Summary

Closes #8750.

Adds SemanticScholarTools, a research toolkit backed by the Semantic Scholar Academic Graph API. It gives Agno agents paper search, paper metadata lookup, and optional author-paper lookup without adding a new package dependency.

Changes

• Add SemanticScholarTools under libs/agno/agno/tools/
• Support search_papers, get_paper, and get_author_papers
• Use existing httpx dependency and optional SEMANTIC_SCHOLAR_API_KEY header support
• Add mock-based unit tests for initialization, request handling, formatting, validation, and error paths
• Add a cookbook example under cookbook/91_tools/

Type of change

• Bug fix
• New feature
• Breaking change
• Improvement
• Model update
• Other:

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Checklist

• Code complies with style guidelines
• Ran format/validation scripts or focused equivalents
• Self-review completed
• Documentation updated through a cookbook example
• Examples and guides: Relevant cookbook examples have been included or updated
• Tested in clean environment
• Tests added/updated

Duplicate and AI-Generated PR Check

• I have searched existing open pull requests and confirmed that no other PR already addresses this issue
• If a similar PR exists, I have explained below why this PR is a better approach
• Check if this PR was entirely AI-generated (by Copilot, Claude Code, Cursor, etc.)

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How Has This Been Tested?

• /tmp/agno-semantic-scholar-venv/bin/python -m pytest libs/agno/tests/unit/tools/test_semantic_scholar.py -q
• /tmp/agno-semantic-scholar-venv/bin/python -m ruff check libs/agno/agno/tools/semantic_scholar.py libs/agno/tests/unit/tools/test_semantic_scholar.py cookbook/91_tools/semantic_scholar_tools.py
• /tmp/agno-semantic-scholar-venv/bin/python -m ruff format --check libs/agno/agno/tools/semantic_scholar.py libs/agno/tests/unit/tools/test_semantic_scholar.py cookbook/91_tools/semantic_scholar_tools.py
• /tmp/agno-semantic-scholar-venv/bin/python -m mypy libs/agno/agno/tools/semantic_scholar.py --config-file libs/agno/pyproject.toml --follow-imports=skip

Additional Notes

Unauthenticated live smoke testing hit Semantic Scholar shared public rate limiting with HTTP 429, so the PR relies on mock-based unit coverage and supports SEMANTIC_SCHOLAR_API_KEY for stable usage.

AI assistance disclosure: This PR was generated with Codex. I reviewed the implementation scope and ran the checks listed above.