Add ChatOptions support to ChatAgentConfig

[OnurGumus]

Summary

• Adds ChatOptions field to ChatAgentConfig and ChatAgent.withChatOptions pipeline function
• Wraps IChatClient with a delegating client that merges default ChatOptions (temperature, top-p, model, etc.) into every call
• Per-call options from MAF override the defaults where present

Motivation

ChatClientAgent's constructor doesn't accept both instructions/tools and ChatOptions. This provides a clean way to set options like temperature at the agent config level.

Usage

ChatAgent.create instructions
|> ChatAgent.withChatOptions (ChatOptions(Temperature = 0.0f))
|> ChatAgent.withTools tools
|> ChatAgent.build chatClient