Fix trace processor registration upstream in OpenAI Agents

The documentation states that we should call `addTraceProcessor` to register a new processor, but it does not work. Instead, we use this workaround and reference the global trace provider directly.

```ts
// this is the official method for registering a trace processor, but it
// does not work.
// addTraceProcessor(processor);

// instead, we get a reference to the global trace provider and register it directly.
const { getGlobalTraceProvider } = moduleExports;
const globalProvider = getGlobalTraceProvider();
globalProvider.registerProcessor(processor);
```