Add built-in support for tool control parameters

[nwumnn]

What this does

Adds tool choice and parallel tool calls options to the with_tool and with_tools method.

Users can now specify:

• choice: control how the model should use tools (auto, none, any, or specific tool name)
• parallel: boolean parameter to allow/disallow parallel tool calls

chat.with_tools(MyTool, choice: :any, parallel: false)
chat.with_tool(SpecificTool, choice: :specific_tool_name, parallel: false)

Also updates the handle_tool_calls method. With :any or specific tool choices, tool results are not automatically sent back to the model to prevent infinite loops.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

Related issues

Fixes #343