Core Refactoring: Headers Decoupling and CMake Migration

[ZedongPeng]

Summary

This PR implements major structural improvements to enhance maintainability and cross-platform support.
These changes are fairly extensive and may affect downstream usage.
Any comments or suggestions are very welcome. @LucasBoTang @jinwen-yang

Changes

1. Build System Migration

• Switched from Makefiles to CMake.
• Benefit: Enables robust cross-platform building (Linux, Windows, macOS) and simplifies external dependency management (CUDA, ZLIB and CUDA_ARCHITECTURES).
• Fixes Support automatic CUDA detection (migrate to CMake) #15

2. Header Separation

• Removed redundant includes.

• Rename interface.c/h to cupdlpx.c/h.

• Headers are now split:

  • include/: Public API (What users see).
  • internal/: Private Implementation (What users don't see).

• Benefit:

  • Achieves stronger encapsulation and reduces unwanted coupling when external projects include our headers.
  • Necessary for developing Julia interface (using Clang.jl to wrap the C API)

• Related PR: [WIP] Add Julia interface for cuPDLPx cuPDLPx.jl#2

This PR has been verified to work withpip install .

$ pip install .
Processing /orcd/home/002/zdpeng/github/cuPDLPx
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Installing backend dependencies ... done
  Preparing metadata (pyproject.toml) ... done
Requirement already satisfied: numpy>=1.21 in /home/zdpeng/anaconda3/lib/python3.12/site-packages (from cupdlpx==0.1.2) (1.26.4)
Requirement already satisfied: scipy>=1.8 in /home/zdpeng/anaconda3/lib/python3.12/site-packages (from cupdlpx==0.1.2) (1.13.1)
Building wheels for collected packages: cupdlpx
  Building wheel for cupdlpx (pyproject.toml) ... done
  Created wheel for cupdlpx: filename=cupdlpx-0.1.2-cp312-cp312-linux_x86_64.whl size=745587 sha256=8dd3b19efe0db53a394e5656258e4d618d92d7011f579b1d443ef504130fbac7
  Stored in directory: /orcd/home/002/zdpeng/tmp/pip-ephem-wheel-cache-mhtou0t7/wheels/9d/09/77/9b7446b72da85c238bb43f7eac35c8f623b17bf9d9cb3a1452
Successfully built cupdlpx
Installing collected packages: cupdlpx
  Attempting uninstall: cupdlpx
    Found existing installation: cupdlpx 0.1.2
    Uninstalling cupdlpx-0.1.2:
      Successfully uninstalled cupdlpx-0.1.2
Successfully installed cupdlpx-0.1.2