Fix loading KV quantization scale; Enable modelopt kv cache (#4686)

Co-authored-by: qingquansong <ustcsqq@gmail.com>

python/sglang/srt/layers/radix_attention.py

@@ -13,8 +13,12 @@
 # ==============================================================================
 """Radix attention."""
 
+from typing import Optional
+
 from torch import nn
 
+from sglang.srt.layers.linear import UnquantizedLinearMethod
+from sglang.srt.layers.quantization.base_config import QuantizationConfig
 from sglang.srt.model_executor.forward_batch_info import ForwardBatch
 
 
@@ -34,6 +38,7 @@ class RadixAttention(nn.Module):
         v_head_dim: int = -1,
         sliding_window_size: int = -1,
         is_cross_attention: bool = False,
+        quant_config: Optional[QuantizationConfig] = None,
         prefix: str = "",
         use_irope: bool = False,
     ):
@@ -49,9 +54,16 @@ class RadixAttention(nn.Module):
         self.logit_cap = logit_cap
         self.sliding_window_size = sliding_window_size or -1
         self.is_cross_attention = is_cross_attention
+        self.use_irope = use_irope
         self.k_scale = None
         self.v_scale = None
-        self.use_irope = use_irope
+        self.k_scale_float = None
+        self.v_scale_float = None
+        self.quant_method = None
+        if quant_config is not None:
+            self.quant_method = quant_config.get_quant_method(self, prefix=prefix)
+        if self.quant_method is not None:
+            self.quant_method.create_weights(self)
 
     def forward(
         self,