Add doc page to learn tool usage in DSPy

[TomeHirata]

Tool call agent is a very common and popular way to implement AI agents. While DSPy supports tool calling in multiple ways, many users don't realize its support due to the lack of documentation. This PR introduces a page for Tools in DSPy to increase the visibility.

[Copilot]

Pull Request Overview

This PR adds comprehensive documentation for tool usage in DSPy to improve visibility and understanding of the framework's tool-calling capabilities. The documentation covers both automated ReAct agents and manual tool handling approaches, providing developers with clear examples and best practices for implementing AI agents that can interact with external functions and services.

• Adds a new "Tools" section to the DSPy programming documentation
• Documents two main approaches: dspy.ReAct for fully managed tool agents and manual tool handling with dspy.Tool and dspy.ToolCalls
• Includes practical examples, best practices, and guidance on when to use each approach

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/mkdocs.yml	Adds the new Tools page to the navigation structure under Programming concepts
docs/docs/learn/programming/tools.md	Creates comprehensive documentation covering ReAct agents, manual tool handling, and implementation best practices

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