fix: that last rank got all the rest

apps/hiopy/_distribute_work.py

@@ -136,9 +136,11 @@ def distribute_work(grouped_data_vars, size):
         result = [(group, variables, slice(None))]
 
         # Add additional groups to this rank until it reaches the byte limit
-        while gsize < bytes_per_rank:
+        while gsize < bytes_per_rank or size == 1:
+            if len(group_sizes) == 0:
+                break
             group, next_gsize = max(group_sizes.items(), key=lambda x: x[1])
-            if gsize + next_gsize > bytes_per_rank:
+            if gsize + next_gsize > bytes_per_rank and size > 1:
                 break
             result.append((group, grouped_data_vars.pop(group), slice(None)))
             del group_sizes[group]