[Attention] MLA move rotary embedding to cuda-graph region

[LucasWilkinson]

Following on from #17484, with: #14770 we are no longer materializing the absorbed matrices so we can move the rotary embeddings into the cuda-graph region lowering CPU overhead:

Perf

Main

CPU time for unified_attention is 216us

PR

CPU time for unified_attention is 149us

Accuracy

VLLM_USE_V1=1 lm-eval --model vllm --model_args pretrained=deepseek-ai/DeepSeek-V2-Lite-Chat,tensor_parallel_size=2,dtype=auto,gpu_memory_utilization=0.9,trust_remote_code=True,max_model_len=16
384 --task gsm8k --num_fewshot 5  --batch_size auto
...
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.6649|±  |0.0130|
|     |       |strict-match    |     5|exact_match|↑  |0.6558|±  |0.0131|

VLLM_USE_V1=0 lm-eval --model vllm --model_args pretrained=deepseek-ai/DeepSeek-V2-Lite-Chat,tensor_parallel_size=2,dtype=auto,gpu_memory_utilization=0.9,trust_remote_code=True,max_model_len=16
384 --task gsm8k --num_fewshot 5  --batch_size auto
...
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.6649|±  |0.0130|
|     |       |strict-match    |     5|exact_match|↑  |0.6550|±  |0.0131|

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[mgoin]

Looks reasonable to me and nice simplifications!