)

## What does this PR do?

**Type of change:**  Feature extention

**Overview:**
Added support to quantize KV cache in vLLM fakequant by adding
quantization support for
[MLAAttention](https://github.com/vllm-project/vllm/blob/v0.11.1/vllm/attention/layer.py#L641)

## Usage
Please refer to
[Readme](https://github.com/NVIDIA/Model-Optimizer/tree/kinjal/vllm_att_quant/examples/vllm_serve#calibrate-and-serve-fake-quant-model-in-vllm)

```shell
KV_QUANT_CFG=NVFP4_KV_CFG QUANT_CFG=NVFP4_DEFAULT_CFG python vllm_serve_fakequant.py deepseek-ai/DeepSeek-V2 --served-model-name deepseek-ai/DeepSeek-V2 --host 0.0.0.0 --port 8001 --trust-remote-code --enforce-eager --gpu-memory-utilization 0.8
```

## Testing
Locally tested KV Cache quantization
```
�(rotary_emb): DeepseekScalingRotaryEmbedding()
�(mla_attn): MultiHeadLatentAttentionWrapper(
�  (fused_qkv_a_proj): QuantMergedColumnParallelLinear(
�    in_features=5120, output_features=2112, bias=False, tp_size=1, gather_output=False
�    (input_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=141.0000 calibrator=MaxCalibrator quant)
�    (weight_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=1.4297 calibrator=MaxCalibrator quant)
�    (output_quantizer): TensorQuantizer(disabled)
�  )
�  (q_a_layernorm): RMSNorm(hidden_size=1536, eps=1e-06)
�  (q_b_proj): QuantColumnParallelLinear(
�    in_features=1536, output_features=3072, bias=False, tp_size=8, gather_output=False
�    (input_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=32.0000 calibrator=MaxCalibrator quant)
�    (weight_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=0.1670 calibrator=MaxCalibrator quant)
�    (output_quantizer): TensorQuantizer(disabled)
�  )
�  (kv_a_layernorm): RMSNorm(hidden_size=512, eps=1e-06)
�  (kv_b_proj): QuantColumnParallelLinear(
�    in_features=512, output_features=4096, bias=False, tp_size=8, gather_output=False
�    (input_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=7.5312 calibrator=MaxCalibrator quant)
�    (weight_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=0.2773 calibrator=MaxCalibrator quant)
�    (output_quantizer): TensorQuantizer(disabled)
�  )
�  (rotary_emb): DeepseekScalingRotaryEmbedding()
�  (o_proj): QuantRowParallelLinear(
�    in_features=2048, output_features=5120, bias=False, tp_size=8, reduce_results=True
�    (input_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=1.7188 calibrator=MaxCalibrator quant)
�    (weight_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=0.4336 calibrator=MaxCalibrator quant)
�    (output_quantizer): TensorQuantizer(disabled)
�  )
�  (mla_attn): QuantMLAAttention(
�    (q_bmm_quantizer): TensorQuantizer(disabled)
�    (kv_c_bmm_quantizer): TensorQuantizer((2, 1) bit fake block_sizes={-1: 16, 'type': 'dynamic', 'scale_bits': (4, 3)}, amax=7.5312 calibrator=MaxCalibrator quant)
�  )
�)
```

## Before your PR is "*Ready for review*"
<!-- If you haven't finished some of the above items you can still open
`Draft` PR. -->

- **Make sure you read and follow [Contributor
guidelines](https://github.com/NVIDIA/Model-Optimizer/blob/main/CONTRIBUTING.md)**
and your commits are signed.
- **Is this change backward compatible?**: Yes
- **Did you write any new necessary tests?**:No
- **Did you add or update any necessary documentation?**:NA
- **Did you update
[Changelog](https://github.com/NVIDIA/Model-Optimizer/blob/main/CHANGELOG.rst)?**:
NA

## Additional Information
<!-- E.g. related issue. -->

---------

Signed-off-by: Kinjal Patel <[email protected]>
Signed-off-by: Chenhan Yu <[email protected]>