HeightMap: add query methods (closes #196)

Add methods to query HeightMap values and statistics:
- get(pos): Get height value at integer coordinates
- get_interpolated(pos): Get bilinearly interpolated height at float coords
- get_slope(pos): Get slope angle (0 to pi/2) at position
- get_normal(pos, water_level): Get surface normal vector
- min_max(): Get (min, max) tuple of all values
- count_in_range(range): Count cells with values in range

All methods include proper bounds checking and error messages.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/PyHeightMap.h

@@ -32,6 +32,14 @@ public:
     static PyObject* clamp(PyHeightMapObject* self, PyObject* args, PyObject* kwds);
     static PyObject* normalize(PyHeightMapObject* self, PyObject* args, PyObject* kwds);
 
+    // Query methods (#196)
+    static PyObject* get(PyHeightMapObject* self, PyObject* args);
+    static PyObject* get_interpolated(PyHeightMapObject* self, PyObject* args);
+    static PyObject* get_slope(PyHeightMapObject* self, PyObject* args);
+    static PyObject* get_normal(PyHeightMapObject* self, PyObject* args, PyObject* kwds);
+    static PyObject* min_max(PyHeightMapObject* self, PyObject* Py_UNUSED(args));
+    static PyObject* count_in_range(PyHeightMapObject* self, PyObject* args);
+
     // Method and property definitions
     static PyMethodDef methods[];
     static PyGetSetDef getsetters[];