modify default value of stride to 64 in the function letterbox

[TommeyChang]

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When the default value of stride is 32, it confronts an error when the width or height of the image is resized to 864.
I fix the bug from setting the stride to 64. Thus, I suggest to change the default value.

🛠️ PR Summary

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🌟 Summary

Change stride value in the letterbox function in augmentation utilities.

📊 Key Changes

• Modified the letterbox function's stride parameter from 32 to 64.

🎯 Purpose & Impact

• Purpose: Adjust the resizing and padding functionality to accommodate different stride requirements.
• Impact: This change could lead to faster processing times and better performance for models optimized with a stride of 64, potentially improving both training and inference speeds for users. 🚀

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