Scope TF imports in DetectMultiBackend()

[phodgers]

As per bug report #5709 I think there should be only one attempt to assign interpreter, and it appears tflite is only ever needed for the case of edgetpu model.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced TensorFlow model loading in YOLOv5 with dynamic imports.

📊 Key Changes

• Dynamic import of TensorFlow library when necessary during different TensorFlow model loadings (.pb, saved_model, tflite).
• Log statements added for clarity on model loading progress, specifically for TensorFlow .pb models.

🎯 Purpose & Impact

• 🚀 Reduces initial load time for users not using TensorFlow models by preventing unnecessary imports.
• 👀 Provides informative logging for users, making it easier to understand what’s happening during model loading.
• 🔍 Streamlines TensorFlow compatibility, offering a more user-friendly and efficient experience for running YOLOv5 with TensorFlow models.

[github-actions]

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[glenn-jocher]

@phodgers PR is merged. Thank you for your contributions to YOLOv5 🚀 and Vision AI ⭐