مستندات فنی API تابلو

You are helping me build a client for the Tablo Gold Price API (tablo.gold).

Base URL: https://tablo.gold
Auth: every request needs an "Authorization: Bearer <API_KEY>" header. Keys look like "tablo_XXXXXXXXXXXX".

Endpoints (all GET, JSON responses, each independently granted per key):
1. /api/v1/gold-prices  — per-platform gram-18k gold prices.
   { generated_at, platforms: [{ platform_slug, price_toman, price_display, updated_at }] }
2. /api/v1/coin-prices  — سکه امامی / نیم‌سکه / ربع‌سکه prices.
   { generated_at, coins: [{ key, label, price_toman, price_display, updated_at }] }
3. /api/v1/bubble-spread — the gram-gold bubble (gap vs. intrinsic value) and the
   spread across platforms. Either field can be null when an input is missing.
   { generated_at, bubble: { toman, updated_at } | null, spread: { toman, display, updated_at } | null }
4. /api/v1/coin-bubble  — the امامی coin's bubble ONLY (half/quarter have no bubble).
   { generated_at, key: "emami", label, coin_bubble: { toman, updated_at } | null }
5. /api/v1/reference    — an independent market reference price, sold as its own product.
   { generated_at, reference_price: { value, read_at, sourceLabel } | null }

Error responses:
- 401 { "error": "invalid or expired api key" }        — missing/unknown/disabled/expired key.
- 403 { "error": "key not authorized for this api" }   — valid key, wrong endpoint.
- 429 { "error": "rate limit exceeded" }                — 60 requests / 60 seconds per key per
                                                            endpoint; a Retry-After header (seconds)
                                                            says how long to back off.
- 503 { "error": "service temporarily unavailable" }    — transient, safe to retry.

Treat any null field (bubble, spread, coin_bubble, reference_price) as "not available right now",
not as an error — never throw on a null value alone.

Please write a client (ask me which language/runtime if it isn't obvious from my project) that:
authenticates with the bearer key, calls only the endpoint(s) I actually need, retries a 429 after
waiting for Retry-After seconds, and treats null fields as legitimately absent data.