Scale request logic

[whoabuddy]

aider + grok 4, impressive so far!

What's been done so far:

• Config (src/config.ts): Parses HIRO_API_KEYS as an array; added methods for DO name hashing and reverse key lookups.
• Main Worker (src/index.ts): Added fast-path KV cache checks for read-only endpoints; implemented round-robin DO selection using KV counter for load balancing.
• Durable Object (src/durable-objects/contract-calls-do.ts): Assigns Hiro API keys by DO ID; forwards keys to fetcher; sets higher priority for non-cache-busting requests.
• Request Queue (src/services/request-queue-service.ts): Added priority field to requests; sorts queue by priority during processing.
• API Services (src/services/stacks-api-service.ts & src/services/stacks-contract-data-service.ts): Updated to accept and use Hiro API keys for authenticated requests.
• Rate Limiting (src/services/token-bucket-service.ts): Added sync from Hiro response headers; updated services to pass and sync headers post-request.
• setup API keys in wrangler secrets

What's left:

• fix failing tests
• add new tests
• test against staging frontend (or preview build)