[BUG] OpenAi `tool_choice` being overridden when using `with_params`

[imtyM]

Basic checks

• I searched existing issues - this hasn't been reported
• I can reproduce this consistently
• This is a RubyLLM bug, not my application code

What's broken?

Setting a custom tool choice param for OpenAi is being overridden and set to tool_choice: "auto" - preventing the possibility of using the tool_choice: "required" feature.
This is due to

ruby_llm/lib/ruby_llm/providers/openai/chat.rb

Lines 24 to 27 in aceeaf2

	if tools.any?
	payload[:tools] = tools.map { |_, tool| tool_for(tool) }
	payload[:tool_choice] = 'auto'
	end

This is related to #303 ("dangerously" setting params), but I think the tool choice in render_payload should be removed?

The open ai docs suggest that it would default to auto if tools are present.

How to reproduce

1. Configure RubyLLM using OpenAi and a model that supports tools e.g. gpt-4o-mini
2. Enable debug to see the request export RUBYLLM_DEBUG=true
3. create and set a tool to the chat instance
4. set a custom tool_choice: 'required' param
5. ask.

Expected behavior

tool_choice should be "required" in the payload.

What actually happened

tool_choice is set to "auto"

Environment

Ruby version: 3.2.3
RubyLLM version: 1.4.0

[tpaulshippy]

Sounds like an easy PR waiting to be written to remove line 26.