Fix an issue in the voter calculator where existing voters were not
retained across data centers and racks in certain scenarios. This
occurred when voters were distributed across more data centers and racks
than the maximum allowed number of voters.
Previously, the prioritization logic for data centers and racks did not
consider the number of existing assigned voters. It only prioritized
nodes within a single data center or rack, which could result in
unnecessary reassignment of voters.
Improved the prioritization logic to account for the number of existing
voters in each data center and rack.
This change ensures a more stable voter distribution and reduces
unnecessary voter reassignments.
Fixes: scylladb/scylladb#23950
2ae59e8a87