Adding a Market Provider

When injecting a new data source into the system, strictly follow the provider abstraction structure.

1. Create the Service File: Navigating to src/market/providers/ and establish a new class implementing the IMarketProvider interface.
2. Wrap in Cache: Instantiate your class exclusively through the CacheService rather than calling it directly within an Express handler.
3. Error Propagation: The provider must trap its own HTTP 400/500 errors and map them to internal structural defaults. If an upstream source fails, it shouldn't crash the server.

typescript
export class ExampleProvider {
  async fetchIndex() {
    try {
      const res = await fetch("...");
      return await res.json();
    } catch {
      return { _fallback: true, data: [] };
    }
  }
}