Improve Error Handling for HTTP 4xx Errors

[KernelDeimos]

Improve Error Handling for HTTP 4xx Errors

Description

This PR improves error handling for HTTP 4xx errors in the fetch tool, particularly for 400 Bad Request and 429 Rate Limit Exceeded errors. It implements retry mechanisms with exponential backoff and adds a "slow mode" feature to help avoid rate limits.

Changes

• Added retry mechanism for 400 Bad Request errors with exponential backoff
• Implemented exponential backoff for 429 Rate Limit Exceeded errors
• Added support for the Retry-After header
• Added "slow mode" that can be enabled automatically after rate limit errors or manually
• Added comprehensive test suite for error handling scenarios
• Added documentation for the fetch tool with examples of the new error handling features

Testing

All tests pass, including the new error handling tests. The implementation has been verified to handle:

• Bad Request (400) errors with retries
• Rate Limit (429) errors with exponential backoff
• Respecting Retry-After headers
• Network errors with retries
• Proper error throwing after maximum retries

Documentation

Added a new documentation file at docs/tools/fetch.md with detailed information about the fetch tool and its error handling capabilities.

Closes #370