Issue #, if available:

Description of changes:
Implement AdaptiveRetryStrategy that extends StandardRetryStrategy with client-side rate limiting using token bucket and CUBIC congestion control algorithm.

Key Changes:

• Add AdaptiveRetryStrategy class with rate limiter integration
• Implement timeout handling for token acquisition that counts as retry attempt
• Integrate rate limiting hooks in RequestPipeline._retry() method
• Add thread-safe async lock to RequestRateTracker.measure_rate()
• Add comprehensive unit and functional tests for adaptive retry behavior

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