Simba Chain Rate Limits

SIMBA acknowledges throttling exists — error code 1429 TOO_MANY_REQUESTS maps to HTTP 429 in its published error reference — but publishes no numeric limit, no window, no scope and no runtime header. Anonymous 200 responses from the Blocks API carry only `server: istio-envoy` and `strict-transport-security`; no RateLimit-*, X-RateLimit-* or Retry-After header was present. An agent therefore has no runtime signal to pace itself with and can only react to a 429 after it happens, with no Retry-After to tell it how long to wait.