Update check_requirements() exclude list

[glenn-jocher]

Adds some non-essential dependencies to the check_requirements() exclude list.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Adjusted dependency checks and lazy imports for specific packages.

📊 Key Changes

• Modified check_requirements calls in detect.py, hubconf.py, test.py, and train.py to exclude checking for 'tensorboard'.
• Shifted the import statement for kmeans from scipy from the top of autoanchor.py file to within the function that requires it.
• Similarly, moved butter and filtfilt scipy imports in plots.py to the function scope where they are used.

🎯 Purpose & Impact

• 🚀 The primary purpose of these changes is to improve the efficiency and modularity of dependency checks, allowing for a more streamlined setup and reducing issues with unused dependencies.
• 🛠 This impacts users by potentially reducing installation times and avoiding errors that occur due to unneeded packages.
• 📦 Moving imports into function scope (lazy loading) is a common pattern when the import is heavy or not always used, which can help in reducing initial load times and saving memory in some scenarios.