Migrate to Zarr 3

Pre-work to #6

This MR has the following:

1. Migration to Zarr 3 API while removing the deprecated yet still supported Zarr 2 API usage.
2. Essential fixes for the main-branch resulting from the learnings out of the global-hackathon exploits (The non-essential ones will be fixed in a seperate branch).

apps/hiopy/tests/CMakeLists.txt

@@ -29,7 +29,7 @@ set_tests_properties(hiopy.create_simple_dataset_4threads PROPERTIES
 
 add_test(
   NAME hiopy.check_hierarchy
-  COMMAND ${Python_EXECUTABLE} "${CMAKE_CURRENT_SOURCE_DIR}/check_hierarchy.py" "simple_dataset.zarr"
+  COMMAND "/usr/bin/env" "python3" "${CMAKE_CURRENT_SOURCE_DIR}/check_hierarchy.py" "simple_dataset.zarr"
 )
 
 set_tests_properties(hiopy.check_hierarchy PROPERTIES