Implement defense against RateLimitError in CodeAgent

[codegen-sh]

Description

This PR implements a defense mechanism against RateLimitError in the CodeAgent class. While the underlying LangGraph implementation already has a retry policy for RateLimitError, the CodeAgent's run method needed to be updated to properly handle these errors when they occur.

Changes

• Added a retry mechanism in the run method of CodeAgent to catch and handle RateLimitError from both Anthropic and OpenAI
• Implemented exponential backoff with jitter for retries
• Added proper error messaging to inform users when rate limits are hit
• Added missing class attributes for SWEBench integration (run_id, instance_id, difficulty)

Testing

The implementation follows the same retry pattern that's already used in the LangGraph implementation, with a maximum of 10 retries, starting with a 30-second delay and exponentially increasing up to a maximum of 1000 seconds between retries.

Fixes CG-11759

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