[WIP] Add reasoning effort support to session configuration

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>session.setModel() missing ReasoningEffort value</issue_title>
<issue_description>When creating or resuming a session you can set both the model and the ReasoningEffort -

SessionConfig config = new()
{
	Model = defaultModel.Id,
	ReasoningEffort = defaultModel.DefaultReasoningEffort
}

This PR added support for selecting a new model during a session, but missing the ability to set the models ReasoningEffort - #621</issue_description>

<agent_instructions>Add reasoning effort and appropriate tests.</agent_instructions>

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