Single port memory assignment using graph coloring sometimes produce execive number of memories

Description of issue:

ProcessCollection::split_ports(heuristic="graph_color", total_ports=1) can sometimes produce too many memories.

Comment:

The attached figure shows an example where ProcessCollection::split_ports(heuristic="graph_color", total_ports=1) produces one too many memories. Clearly, Proc. 783 would fit in both Memory 1 and Memory 3 and so only two memories in total should be required after the split.