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/worker.py

@@ -115,13 +115,13 @@ def main():
         gid: Coyote(f"{args.process_group}_{gid}") for gid, data_vars, chunk_slice in my_data_vars
     }
 
+    data_handlers = []
+
     for gid, data_vars, chunk_slice in my_data_vars:
         coyote = coyote_instances[gid]
         # all vars in data_vars define the same grid
         def_grid(coyote, data_vars[0], chunk_slice)
 
-        data_handlers = []
-
         for v in data_vars:
             # compute timestep
             var_group = get_var_group(v)