NKI Library renames the kv_parallel_segmented_prefill kernel starting with Neuron 2.31.0

Starting with Neuron SDK 2.31.0, the NKI Library kv_parallel_segmented_prefill kernel has been renamed to attention_kv_parallel_segmented_cte. The source file moves from core/attention/kv_parallel_segmented_prefill.py to core/attention/attention_kv_parallel_segmented_cte.py.

Callers must update both their import path and the function name. For the kernel reference, see Attention KV-Parallel Segmented CTE.