重构: 采用模块化 src 布局

- 重组代码为模块化结构：lbm/, common/, cuda/
- LBM 相关代码移至 src/CelerisLab/lbm/
- 通用工具移至 src/CelerisLab/common/
- CUDA 编译器移至 src/CelerisLab/cuda/
- 更新所有导入路径以适配新结构
- 提供灵活的导入接口（直接导入/模块导入/命名空间风格）
- 为未来扩展（FEM, SPH, MPM 等）做好准备

pyproject.toml

@@ -35,9 +35,6 @@ dependencies = [
 Homepage = "https://github.com/frank14f/CelerisLab"
 Repository = "https://github.com/frank14f/CelerisLab.git"
 
-[project.scripts]
-celerislab = "CelerisLab.driver:main"
-
 [tool.setuptools]
 package-dir = {"" = "src"}
 
@@ -45,4 +42,4 @@ package-dir = {"" = "src"}
 where = ["src"]
 
 [tool.setuptools.package-data]
-CelerisLab = ["kernels/*.cu", "kernels/*.h", "configs/*.json"]
+"CelerisLab.lbm" = ["kernels/*.cu", "kernels/*.h", "configs/*.json"]