feat(client): add handle429Backoff method for intelligent rate limit handling

changelog.md

@@ -1,5 +1,24 @@
 # Changelog
 
+## 2025-07-29 - 4.2.0 - feat(client)
+Add handle429Backoff method for intelligent rate limit handling
+
+**Features:**
+- Added `handle429Backoff()` method to SmartRequest class for automatic HTTP 429 handling
+- Respects `Retry-After` headers with support for both seconds and HTTP date formats
+- Configurable exponential backoff when no Retry-After header is present
+- Added `RateLimitConfig` interface with customizable retry behavior
+- Optional callback for monitoring rate limit events
+- Maximum wait time capping to prevent excessive delays
+
+**Improvements:**
+- Updated test endpoints to use more reliable services (jsonplaceholder, echo.zuplo.io)
+- Added timeout parameter to test script for better CI/CD compatibility
+
+**Documentation:**
+- Added comprehensive rate limiting section to README with examples
+- Documented all configuration options for handle429Backoff
+
 ## 2025-07-29 - 4.1.0 - feat(client)
 Add missing options() method to SmartRequest client