Add reasoningEffort param and Developer enum in Role

[chsword]

ChatRequest:

reasoning_effort
string

Optional
Defaults to medium
o1 models only

Constrains effort on reasoning for [reasoning models](https://platform.openai.com/docs/guides/reasoning). Currently supported values are low, medium, and high. Reducing reasoning effort can result in faster responses and fewer tokens used on reasoning in a response.

Role enum:

Developer message
object
Developer-provided instructions that the model should follow, regardless of messages sent by the user. With o1 models and newer, developer messages replace the previous system messages.

[StephenHodgson]

Please add unit tests and increment version number and update change notes

[StephenHodgson]

is this needed?

Suggested change

using System.Data;

[StephenHodgson]

Addressed in #404