fix(client): explicitly copy fetch in withOptions

Author: stainless-app[bot]

src/client.ts

@@ -301,6 +301,7 @@ export class LlamaStackClient {
       timeout: this.timeout,
       logger: this.logger,
       logLevel: this.logLevel,
+      fetch: this.fetch,
       fetchOptions: this.fetchOptions,
       apiKey: this.apiKey,
       ...options,