Support TP > GQA for inference

[santhnm2]

What does this PR do ?

Fixes an issue in the KV cache allocation to support TP > GQA (clamps num_attention_heads_per_partition to 1).

Contribution process

flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
        C1[Expert Review] --> C2[Final Review]
    end
    B --> C1
    C2 --> D[Merge]

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[santhnm2]

/ok to test 82ee43b

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/22457413528