Fix/preflight NUMA imbalance to mean uneven GPU distribution across nodes

[alexsu52]

Changes:

Only flag imbalance if the COUNT of GPUs on each node differs.
Example:
4 on Node 0, 4 on Node 1 -> counts=[4,4] -> set={4} -> len=1 -> NOT imbalanced.
7 on Node 0, 1 on Node 1 -> counts=[7,1] -> set={7,1} -> len=2 -> Imbalanced.

Reason for changes:

The previous logic would issue a NUMA imbalance warning if not all GPUs were connected to the same node, resulting in a false positive when using a multi-socket CPU.

[Copilot]

Pull request overview

This PR fixes a false positive NUMA imbalance warning that occurred when GPUs were distributed across multiple NUMA nodes in a balanced manner (e.g., multi-socket CPUs with equal GPU counts per socket). The logic now correctly identifies imbalance only when GPU counts differ between nodes.

Changes:

• Updated NUMA imbalance detection logic to check for uneven GPU distribution across nodes rather than merely checking if GPUs span multiple nodes