Performance Improvement

### Fix API response compatibility issues (v0.1.1) - Make id, object, created fields optional in ChatCompletion - Make id, object, created, model fields optional in ChatCompletionChunk - Make Usage fields optional to handle empty usage objects in streaming - Fix streaming by using httpx send() with stream=True instead of stream context manager Tested with real API calls: - Chat completions: working - Streaming: working - Embeddings: working - Tool calling: working