Update 8.2.1 to working with ToolCalls and RunSteps

[pappde]

• Assistants:
• renamed ToolCallType.Retrieval to FileSearch to match API update
• RunSteps: add service reference and fix StepDetails
• added to IBetaService
• Status: noted in comment that may return "incomplete"
• RunStepList() - request param to optional
• RunStepResponse: changed to original StepDetails (with MessageCreation.MessageId) to match API responses
• NOTE: removed previous StepDetails, but could add back in commented out