Create RETRY_AND_RATE_LIMITS.md

[bigrosss]

Documented safe retry and rate-limit handling patterns so client integrations behave predictably under load.

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Note

Introduces guidance for safe retries and rate-limit handling when using the CLOB API.

• Adds docs/RETRY_AND_RATE_LIMITS.md detailing rate limiting (HTTP 429) and a recommended retry strategy
• Recommended defaults: max retries 3, 250 ms initial delay, exponential backoff; retry on 429/502/503/504 and network timeouts; avoid retries on invalid/auth/order validation errors
• Client guidance: avoid non-idempotent retries, log retry attempts with context, and consider client-side throttling

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