Implement BrowseWeb tool similar to LinearViewIssue tool

[codegen-sh]

This PR implements a new BrowseWeb tool that allows Codegen to browse the web, similar to the LinearViewIssue tool.

Changes:

• Added a new web module in src/codegen/extensions/tools/web/
• Implemented two main tools:
  • web_search_tool: Searches the web and returns content snippets from search results
  • web_view_page_tool: Views the content of a specific webpage
• Added necessary dependencies:
  • beautifulsoup4 for HTML parsing
  • responses for testing
• Added unit tests for the new tools

Implementation Details:

• The web search tool currently returns mock data, but is designed to be easily extended to use a real search API
• The web view page tool uses requests and BeautifulSoup to fetch and parse web pages
• Both tools follow the same pattern as other tools in the codebase, returning Observation objects

Next Steps:

• Integrate with a real search API (Google Custom Search, Bing Search, etc.)
• Add more advanced web scraping capabilities
• Improve error handling and rate limiting