Optimize Lazy Camera Loading for Efficient Compression of Large Files with Numerous Images and Corresponding Cameras (#8)

[EtaCassiopeia]

• Implemented LazyCameraLoader class in camera_utils.py to enable on-demand loading and unloading of cameras.
• Refactored calc_importance function to use LazyCameraLoader for efficient memory management.
• Modified finetune function to leverage LazyCameraLoader and ensure memory is freed after processing each camera.
• Improved memory usage and performance during sensitivity calculation and finetuning processes.
• This solution is particularly beneficial for handling large files and datasets, though it may not be as efficient for smaller datasets.

This commit addresses issue #8.