(feature/fvdb) Build error in a non-conda env

[jamesfisher-geo]

Describe the bug

A build error is thrown when building the Dockerfile. It is caused by these lines, which access conda environment variables.

To fix this behavior

if is_conda_env:
        # Set CUDA_INC_PATH from the appropriate conda target cross-compilation platform directory
        # NOTE: This strategy will potentially have to change when compiling for different platforms but by then we will likely not be using setuptools…
        target_platform_include_dir = (
            Path(os.getenv("CONDA_PREFIX")) / "targets" / f"{platform.machine()}-{platform.system().lower()}" / "include"
        )
        # The cuda-toolkit headers (and other '-dev' package headers) from the packages on the `conda-forge` channel are installed in the `targets` directory
        #   which is to support cross-compilation for different platforms. The headers are installed in the appropriate target platform directory.
        if (target_platform_include_dir / "cuda.h").exists():
            os.environ["CUDA_INC_PATH"] = str(target_platform_include_dir)

To Reproduce

Steps to reproduce the behavior:

1. Build with docker build -t fvdb/prod .

Expected behavior

(A clear and concise description of what you expected to happen.)

Additional context

(Add any other context about the problem here.)