feat: Add tool calling support to GitHub Copilot Chat

[plusplusoneplusplus]

Overview

This PR implements comprehensive tool calling functionality for the GitHub Copilot Chat integration, enabling support for OpenAI-style tool calling patterns.

Changes Made

Core Tool Calling Infrastructure

• New _handle_tool_calls() method: Processes tool calls from the model and executes appropriate functions
• Enhanced send_message() method: Now accepts optional tools parameter and handles tool call workflows
• JSON Response Format: Switched from streaming to JSON responses for better tool call parsing

Echo Tool Implementation

• _execute_echo_tool() method: Demonstration tool that wraps input text in custom XML tags
• get_echo_tool_definition() function: Provides OpenAI-compatible tool definition
• Tool execution logging: Visual feedback for tool call execution

User Experience Improvements

• --tool-demo flag: Interactive demonstration of tool usage capabilities
• Enhanced chat history: Displays tool calls in conversation history with visual indicators
• Tool availability display: Shows available tools in interactive sessions
• Improved error handling: Better error messages for tool call failures and JSON parsing issues

Integration Enhancements

• Default tool inclusion: Echo tool is included by default in both interactive chat and single message modes
• Recursive tool handling: Supports multiple rounds of tool calls within a single conversation
• Tool call visualization: Clear display of tool calls with function names and arguments

Technical Details

The implementation follows OpenAI tool calling specification with proper tool definitions, call IDs, and response formatting.

Testing

All functionality has been tested including tool definition parsing, execution, error handling, and integration with existing chat functionality.

Breaking Changes

None. All changes are backward compatible.

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