Implement client-side rate limiting for adaptive retries.

[ubaskota]

Issue #, if available:

Description of changes:
Implements client-side rate limiting for Adaptive Retries.

Core Components:

• ClientRateLimiter: Orchestrates rate limiting using token bucket and CUBIC algorithm
• CubicCalculator: Implements CUBIC congestion control (70% reduction on throttle, cubic scaling on success)
• RequestRateTracker: Measures actual client request rates using time-bucketed exponential smoothing

Testing:

• All tests pass with proper mocking to avoid time
• Edge case testing for throttling, success responses, and rate capping are covered.
• Type checking and linting pass without errors.

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