Change nvcc and c flags to c++17 for posix systems on extensions/cuda/setup.py

[atakan-topaloglu]

Using nerfstudio, CUDA extension compilation tries to use C++17 features (such as 'if constexpr') but setup.py specified std=c++14.

[atakan-topaloglu]

Fix Number 2 7699b4e

When running rendering, the pipeline attempted to move the ZipNerfDataManager to a specific device before the ray generators were properly initialized. This caused an AttributeError because train_ray_generator didn't exist yet:

AttributeError: 'ZipNerfDataManager' object has no attribute 'train_ray_generator'

The to(device) method was being called in the pipeline initialization before the DataManager's setup methods had a chance to create the ray generators.
Modified the to() method in ZipNerfDataManager to safely handle cases where ray generators haven't been initialized yet.