Support automatic CUDA detection (migrate to CMake)

## Description:
Currently cuPDLPx relies on a `Makefile`, which requires manually setting `CUDA_HOME` and library paths to build with GPU support. The `Makefile` does not support automatic `CUDA` detection.

## Request:
Migrate the build system to `CMake`, and add support for automatic `CUDA` detection with [FindCUDAToolkit](https://cmake.org/cmake/help/latest/module/FindCUDAToolkit.html).