feat(intel-dcap-api): add automatic retry logic for 429 rate limiting

- Add `max_retries` field to ApiClient with default of 3 retries
- Implement `execute_with_retry()` helper method in helpers.rs
- Update all HTTP requests to use retry wrapper for automatic 429 handling
- Add `TooManyRequests` error variant with request_id and retry_after fields
- Respect Retry-After header duration before retrying requests
- Add `set_max_retries()` method to configure retry behavior (0 disables)
- Update documentation and add handle_rate_limit example
- Enhanced error handling in check_status() for 429 responses

The client now transparently handles Intel API rate limiting while remaining
configurable for users who need different retry behavior or manual handling.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Harald Hoyer <harald@matterlabs.dev>

crates/intel-dcap-api/src/client/pck_crl.rs

@@ -49,7 +49,7 @@ impl ApiClient {
         }
 
         let request_builder = self.client.get(url);
-        let response = request_builder.send().await?;
+        let response = self.execute_with_retry(request_builder).await?;
         let response = check_status(response, &[StatusCode::OK]).await?;
 
         let issuer_chain = self.get_required_header(