Add support for array_t<handle> and array_t<object> (#5427)

* Add support for array_t<handle> and array_t<object>

* style: pre-commit fixes

* Remove loops that aren't strictly needed

* Fix compiler warning

* Disable GC-dependent checks when running on pypy or graalpy

* style: pre-commit fixes

* Remove PyValueHolder counter again

* Move tests to templates to avoid code duplication

* Rerun pre-commit

* Restore import that was erroneously removed by pre-commit

* Reduce code duplication with more template magic

* Bring back `.attr("value")` in `return_array_cpp_loop()`

This was meant to further stress-test correctness of refcount handling.

All modified test functions were manually leak-checked (`while True`, top command, Python 3.12.3, Ubuntu 24.01, gcc 13.2.0).

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>

include/pybind11/numpy.h

@@ -1428,7 +1428,11 @@ public:
 };
 
 template <typename T>
-struct npy_format_descriptor<T, enable_if_t<is_same_ignoring_cvref<T, PyObject *>::value>> {
+struct npy_format_descriptor<
+    T,
+    enable_if_t<is_same_ignoring_cvref<T, PyObject *>::value
+                || ((std::is_same<T, handle>::value || std::is_same<T, object>::value)
+                    && sizeof(T) == sizeof(PyObject *))>> {
     static constexpr auto name = const_name("object");
 
     static constexpr int value = npy_api::NPY_OBJECT_;