refactor: numpycpp-style native/pycpp split, remove _impl.h, drop non-Python APIs

- shapely/geometry/*.h: pure native C++ (zero pybind11), raw pointer ctors
- shapely/ops/nearest_points.h: native ops
- Deleted old geometry/, ops/ dirs (pybind11-dependent)
- Deleted ext/distance_to_multigeom (not in Python shapely)
- Deleted Polygon::exterior_coords(), intersection_area() (not in Python)
- Renamed Point::x_/y_ to x/y
- All _impl.h merged into single headers (matching numpycpp pattern)
- Fixed abbreviated variable names, added per-function Python source comments
- All 101 tests pass

Author: peng.li24

CMakeLists.txt

@@ -28,7 +28,8 @@ target_include_directories(shapelycpp INTERFACE
 target_compile_features(shapelycpp INTERFACE cxx_std_17)
 
 # ---- Install — header-only C++ library --------------------------------------
-install(DIRECTORY geometry ops
+# shapely/     — pure native C++ (zero pybind11 dependency)
+install(DIRECTORY shapely
     DESTINATION include/shapelycpp
     FILES_MATCHING PATTERN "*.h"
 )

README.md

@@ -71,21 +71,20 @@ Add `-Ipath/to/shapelycpp` to your compiler flags and include the headers direct
 
 ```
 shapelycpp/
-├── geometry/           # shapely.geometry.* equivalents
-│   ├── point.h
-│   ├── point_impl.h
-│   ├── linestring.h
-│   ├── linestring_impl.h
-│   ├── polygon.h
-│   └── polygon_impl.h
-├── ops/                # shapely.ops.* equivalents
-│   ├── nearest_points.h
-│   ├── nearest_points_impl.h
-│   ├── distance_to_multigeom.h
-│   └── distance_to_multigeom_impl.h
-├── example/            # usage examples
+├── shapely/            # pure native C++ (zero pybind11 dependency)
+│   ├── geometry/
+│   │   ├── point.h
+│   │   ├── linestring.h
+│   │   └── polygon.h
+│   └── ops/
+│       └── nearest_points.h
+├── example/            # native C++ usage examples
 │   ├── CMakeLists.txt
 │   └── main.cpp
+├── tests/              # Python precision alignment tests
+│   ├── module.cpp      # pybind11 test module
+│   ├── test_geometry.py
+│   └── test_ops.py
 ├── CMakeLists.txt      # build & .deb packaging
 └── README.md
 ```

example/main.cpp

@@ -1,3 +1,6 @@
+// C++ 特有文件，Python 端无直接对应。
+// shapelycpp pure native C++ 使用示例 (zero pybind11 dependency).
+
 #include <iostream>
 #include "shapely/geometry/point.h"
 #include "shapely/geometry/linestring.h"