Add exponential backoff support to Job.join() polling

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Summary

Added optional exponential backoff support to the Job.join() method for more efficient polling of task completion. This allows clients to reduce server load by gradually increasing wait times between status checks.

Key Changes

• Added backoff parameter to Job.join() method (default: False for backward compatibility)
• When backoff=True, polling intervals start at 1 second and double with each check, capped at 10 seconds
• When backoff=False, preserves existing behavior with fixed 3-second intervals
• Backoff works seamlessly with existing features:
  • maximum_time timeout still enforced correctly
  • on_check callback receives accurate cumulative elapsed times
• Comprehensive test coverage for backoff behavior, timeout handling, and callback integration

Implementation Details

• Backoff schedule: 1s → 2s → 4s → 8s → 10s → 10s (capped)
• Elapsed time tracking remains accurate regardless of backoff state
• No breaking changes to existing API

https://claude.ai/code/session_01635dq7fRyq8VBZr1mgsU9C