fix: ensure UTF-8 encoding for Windows environments

[vcfgv]

closes #98

[Copilot]

Pull Request Overview

This PR fixes UTF-8 encoding issues specifically for Windows environments by setting the PYTHONIOENCODING environment variable. This addresses potential character encoding problems that could occur when running the ValueCell package on Windows systems.

• Adds OS detection to identify Windows environments
• Sets UTF-8 encoding environment variable for Windows systems
• Removes the automatic agent import statement

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