feat: add linestring() overload for std::vector<std::array<double,2>>

C++ callers can now pass native coordinate lists directly without
needing a numpy intermediate (list_to_numpy_line bridge).

- Add #include <array> to geometry_py.h
- New inline linestring(const std::vector<std::array<double,2>>& pts)
  flattens 2D points into a linear buffer and constructs LineString<double>

Author: peng.li24

.gitignore

@@ -1,7 +1,7 @@
 # Build directories
 build/
 cmake-build-*/
-
+issue/
 # Compiled output
 *.o
 *.so

pycpp/geometry_py.h

@@ -21,6 +21,7 @@
 #include "../shapely/geometry/multipolygon.h"
 #include "../shapely/geometry/geometrycollection.h"
 
+#include <array>
 #include <cstring>
 #include <tuple>
 #include <vector>
@@ -153,6 +154,19 @@ inline LineString<double> linestring(const py::array& arr) {
     return LineString<double>(tmp.data(), static_cast<size_t>(n), 2);
 }
 
+// Accept native C++ coordinate list: std::vector<std::array<double, 2>>
+// No numpy intermediate — flattens directly into LineString<double>.
+inline LineString<double> linestring(const std::vector<std::array<double, 2>>& pts) {
+    if (pts.size() < 2)
+        throw std::runtime_error("LineString: rows must be >= 2");
+    std::vector<double> flat(pts.size() * 2);
+    for (size_t i = 0; i < pts.size(); ++i) {
+        flat[i * 2] = pts[i][0];
+        flat[i * 2 + 1] = pts[i][1];
+    }
+    return LineString<double>(flat.data(), pts.size(), 2);
+}
+
 // -- Polygon --
 inline Polygon<double> polygon(const py::array_t<double>& arr) {
     auto buf = arr.request();