feat: Add Tavily extract function for URL content extraction

[goshanraj-g]

Description

This integration allows LlamaIndex to use the Tavily extract function from the Tavily API to extract raw content from specific URLs.

Changes Made

• ✅ Added extract() method to TavilyToolSpec for extracting raw content from URLs
• ✅ Updated spec_functions to include both "search" and "extract" methods
• ✅ Added comprehensive unit tests (10 unit tests total) with proper mocking
• ✅ Updated README.md with detailed extract function documentation and examples
• ✅ Enhanced example notebook with extract function demonstration
• ✅ Bumped version from 0.4.1 to 0.4.2
• ✅ Fixed docstring formatting to follow Python conventions

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran uv run make format; uv run make lint to appease the lint gods

Testing Results

All 10 tests pass:

• test_class - Inheritance verification
• test_spec_functions - Function specification validation
• test_init - Initialization with API key
• test_search - Search functionality
• test_search_with_default_max_results - Default parameters
• test_extract - Extract functionality
• test_extract_with_defaults - Extract default parameters
• test_extract_empty_results - Empty results handling
• test_extract_missing_fields - Missing field handling
• test_extract_no_results_key - Error condition handling

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[logan-markewich]

Feel free to ignore the failing check, gotta investigate whats up there