Add option "--expand-tools-even-if-tool-choice-none"

[okdshin]

Add option to include tool definitions even when tool_choice is 'none'

Summary

This PR adds a new command-line option --expand-tools-even-if-tool-choice-none which allows including tool definitions in prompts even when tool_choice='none'.

Motivation

In the current implementation, when tool_choice is set to 'none', all tool definitions are removed from the request, preventing the model from seeing the tool schemas. This change enables a workflow where:

1. The model can be aware of available tools (via their definitions in the prompt)
2. But is not expected to use them automatically (since tool_choice='none')

This is useful for:

• Models that need to "plan" about available tools before using them in subsequent requests
• Cases where tool descriptions provide useful context even if the tools aren't used
• Situations where you want the model to reference tool capabilities in its response without actually calling them

Implementation

• Added a new CLI flag --expand-tools-even-if-tool-choice-none (default: False)
• Modified the request validation in protocol.py to no longer remove tools when tool_choice='none'
• Added the new parameter to OpenAIServingChat and passed it through from the API server

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