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/lib.rs

@@ -8,6 +8,14 @@
 //!
 //! Create an [`ApiClient`] to interface with the Intel API.
 //!
+//! # Rate Limiting
+//!
+//! The Intel API implements rate limiting and may return HTTP 429 (Too Many Requests) responses.
+//! This client automatically handles rate limiting by retrying requests up to 3 times by default,
+//! waiting for the duration specified in the `Retry-After` header. You can configure the retry
+//! behavior using [`ApiClient::set_max_retries`]. If all retries are exhausted, the client
+//! returns an [`IntelApiError::TooManyRequests`] error.
+//!
 //! Example
 //! ```rust,no_run
 //! use intel_dcap_api::{ApiClient, IntelApiError, TcbInfoResponse};