[olaams-tech]

Summary

Adds distinct handling for RPC rate limits.

• HttpTransport detects HTTP 429 Too Many Requests and returns a typed DevkitError::RateLimited carrying the numeric Retry-After delay instead of a generic I/O error.
• Client retries rate-limit responses only while the requested delay fits inside a configurable cumulative cap (RetryPolicy::max_rate_limit_wait, 60s by default). A missing or non-numeric Retry-After falls back to a bounded 1s backoff.
• If the requested wait would exceed the cap, the client returns a clear rate-limit error immediately and never sleeps past the cap.
• The CLI maps the new error category to rate_limited; the JSON error envelope and exit code are unchanged.

Tests

• Mocked 429 responses assert retry-then-success and retry exhaustion.
• A local HTTP server test exercises the real HttpTransport 429 path and Retry-After parsing.
• Cap-exceeded behavior is tested without real waiting.
• Retry-After parsing covers seconds, whitespace, and unsupported HTTP-date values.

Verification

cargo fmt --all -- --check
cargo clippy --all-targets --all-features -- -D warnings
cargo test --all

All pass.

Closes #45