(feat) implement decay-based rate limiting in AsyncRequestContext #7481

Summary

This PR adds support for decay-based rate limits in the AsyncThrottler, addressing issue https://github.com/hummingbot/hummingbot/issues/4163. These limits differ from fixed window limits as they continuously recover capacity over time instead of resetting at fixed intervals.

Key design principle: Added this functionality without breaking existing code. Backward compatible with zero changes needed for existing connectors for easy and fast integration.

Rationale

Exchanges like Kraken and Coinbase Pro use decay-based rate limiting rather than traditional fixed windows. Adding this functionality allows connectors to more accurately model these API behaviors and optimize request throughput.

Github Link

https://github.com/hummingbot/hummingbot/pull/7481