feat: Add iteration utilities for iterating over native arrays (#111)

This PR adds minimal STL iterators that can be used to iterate over
GeoArrow memory. The idea is to allow forward iteration from C++ (as
opposed to visitor-style iteration from C or C++). An example from the
tests:

```c
    geoarrow::ArrayReader reader(type);
    reader.SetArray(&array);

    geoarrow::array::MultiPolygonArray<XY> native_array;
    ASSERT_EQ(native_array.Init(reader.View().array_view()), GEOARROW_OK);

    std::vector<std::vector<std::vector<std::vector<XY>>>> multipolygons;
    for (const auto& multipolygon : native_array.value) {
      std::vector<std::vector<std::vector<XY>>> polygons;
      for (const auto& polygon : multipolygon) {
        std::vector<std::vector<XY>> rings;
        for (const auto& ring : polygon) {
          std::vector<XY> coords;
          for (const auto& coord : ring) {
            coords.push_back(coord);
          }
          rings.push_back(std::move(coords));
        }
        polygons.push_back(std::move(rings));
      }
      multipolygons.push_back(std::move(polygons));
    }
```

I think the iterators need a few more overloads to be truly random
access iterators, but the idea is there and they can be improved with
time.

All of these are currently "just structs" intended for very low-level
iteration (not necessary a pretty user-facing interface).

CMakeLists.txt

@@ -29,9 +29,7 @@ else()
   set(GEOARROW_NAMESPACE_DEFINE "// #define GEOARROW_NAMESPACE YourNamespaceHere")
 endif()
 
-if(GEOARROW_BUILD_TESTS)
-  add_library(geoarrow_coverage_config INTERFACE)
-endif()
+add_library(geoarrow_coverage_config INTERFACE)
 
 if(GEOARROW_CODE_COVERAGE)
   target_compile_options(geoarrow_coverage_config INTERFACE -O0 -g --coverage)
@@ -276,6 +274,7 @@ if(GEOARROW_BUILD_TESTS)
   add_executable(hpp_geometry_data_type_test src/geoarrow/hpp/geometry_data_type_test.cc)
   add_executable(hpp_arrow_extension_type_test
                  src/geoarrow/hpp/arrow_extension_type_test.cc)
+  add_executable(hpp_array_util_test src/geoarrow/hpp/array_util_test.cc)
 
   target_link_libraries(geoarrow_type_inline_test geoarrow gtest_main
                         nanoarrow::nanoarrow)
@@ -304,6 +303,11 @@ if(GEOARROW_BUILD_TESTS)
                         nanoarrow::nanoarrow)
   target_link_libraries(hpp_arrow_extension_type_test geoarrow ${GEOARROW_ARROW_TARGET}
                         gtest_main)
+  target_link_libraries(hpp_array_util_test
+                        geoarrow
+                        gtest_main
+                        gmock_main
+                        nanoarrow::nanoarrow)
 
   include(GoogleTest)
   gtest_discover_tests(geoarrow_type_inline_test)
@@ -326,4 +330,5 @@ if(GEOARROW_BUILD_TESTS)
   gtest_discover_tests(hpp_array_writer_test)
   gtest_discover_tests(hpp_geometry_data_type_test)
   gtest_discover_tests(hpp_arrow_extension_type_test)
+  gtest_discover_tests(hpp_array_util_test)
 endif()

src/geoarrow/hpp/array_reader.hpp

@@ -48,10 +48,6 @@ class ArrayReader {
   void SetArray(struct ArrowArray* array) {
     struct GeoArrowError error {};
     GEOARROW_THROW_NOT_OK(&error, GeoArrowArrayReaderSetArray(&reader_, array, &error));
-    if (array_.array.release != nullptr) {
-      array_.array.release(&array_.array);
-    }
-
     std::memcpy(&array_, array, sizeof(struct ArrowArray));
     array->release = nullptr;
   }