feat(genai): add thinking samples

[jdomingr]

Add samples for thinking:

• Thinking with text
• Thinking budget with text
• Thinking including thoughts

All local tests have passed

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• genai/api/GenAI.Samples/Thinking/ThinkingBudgetWithTxt.cs:17, tag googlegenaisdk_thinking_budget_with_txt
• genai/api/GenAI.Samples/Thinking/ThinkingIncludeThoughtsWithTxt.cs:17, tag googlegenaisdk_thinking_includethoughts_with_txt
• genai/api/GenAI.Samples/Thinking/ThinkingWithTxt.cs:17, tag googlegenaisdk_thinking_with_txt

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[gemini-code-assist]

Summary of Changes

Hello @jdomingr, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the GenAI SDK's sample collection by introducing new examples focused on the model's 'thinking' functionalities. These additions provide developers with practical demonstrations of how to interact with advanced content generation features, such as managing the model's internal reasoning budget and accessing its step-by-step thought process, thereby enriching the SDK's educational resources and guiding users in leveraging these powerful capabilities.

Highlights

• New Thinking Samples Added: Three new samples have been introduced to demonstrate various 'thinking' capabilities of the GenAI SDK.
• Thinking Budget Control: A new sample showcases how to configure a 'thinking budget' for content generation, allowing control over the computational resources or steps the model uses for internal reasoning.
• Accessing Model Thoughts: A sample has been added that demonstrates how to explicitly include and retrieve the model's internal 'thoughts' during content generation, providing insight into its reasoning process.
• Basic Text Thinking Sample: A foundational sample for general text-based thinking has been included, illustrating the default behavior of the GenAI model when processing prompts.

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[gemini-code-assist]

Code Review

This pull request introduces new samples demonstrating the 'thinking' feature of the GenAI SDK. The overall structure is good, but I've identified some critical issues related to unsafe access of API responses across all new samples. This could lead to runtime exceptions if the model returns no content. I have provided suggestions to add robust checks for these scenarios. Additionally, I've recommended a correction for the ThinkingIncludeThoughtsWithTxt sample to ensure its logic for handling and returning response data is correct and consistent with its purpose.