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

readme.md

@@ -361,6 +361,69 @@ async function performMultipleRequests() {
 }
 ```
 
+### Rate Limiting (429 Too Many Requests) Handling
+
+The library includes built-in support for handling HTTP 429 (Too Many Requests) responses with intelligent backoff:
+
+```typescript
+import { SmartRequest } from '@push.rocks/smartrequest';
+
+// Simple usage - handle 429 with defaults
+async function fetchWithRateLimitHandling() {
+  const response = await SmartRequest.create()
+    .url('https://api.example.com/data')
+    .handle429Backoff()  // Automatically retry on 429
+    .get();
+
+  return await response.json();
+}
+
+// Advanced usage with custom configuration
+async function fetchWithCustomRateLimiting() {
+  const response = await SmartRequest.create()
+    .url('https://api.example.com/data')
+    .handle429Backoff({
+      maxRetries: 5,              // Try up to 5 times (default: 3)
+      respectRetryAfter: true,    // Honor Retry-After header (default: true)
+      maxWaitTime: 30000,         // Max 30 seconds wait (default: 60000)
+      fallbackDelay: 2000,        // 2s initial delay if no Retry-After (default: 1000)
+      backoffFactor: 2,           // Exponential backoff multiplier (default: 2)
+      onRateLimit: (attempt, waitTime) => {
+        console.log(`Rate limited. Attempt ${attempt}, waiting ${waitTime}ms`);
+      }
+    })
+    .get();
+
+  return await response.json();
+}
+
+// Example: API client with rate limit handling
+class RateLimitedApiClient {
+  private async request(path: string) {
+    return SmartRequest.create()
+      .url(`https://api.example.com${path}`)
+      .handle429Backoff({
+        maxRetries: 3,
+        onRateLimit: (attempt, waitTime) => {
+          console.log(`API rate limit hit. Waiting ${waitTime}ms before retry ${attempt}`);
+        }
+      });
+  }
+
+  async fetchData(id: string) {
+    const response = await this.request(`/data/${id}`).get();
+    return response.json();
+  }
+}
+```
+
+The rate limiting feature:
+- Automatically detects 429 responses and retries with backoff
+- Respects the `Retry-After` header when present (supports both seconds and HTTP date formats)
+- Uses exponential backoff when no `Retry-After` header is provided
+- Allows custom callbacks for monitoring rate limit events
+- Caps maximum wait time to prevent excessive delays
+
 ## Platform-Specific Features
 
 ### Browser-Specific Options