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

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

python/sglang/srt/models/deepseek_v2.py

@@ -489,6 +489,7 @@ class DeepseekV2Attention(nn.Module):
             self.scaling,
             num_kv_heads=self.num_local_heads,
             layer_id=layer_id,
+            quant_config=quant_config,
             prefix=add_prefix("attn", prefix),
         )
 
@@ -669,6 +670,7 @@ class DeepseekV2AttentionMLA(nn.Module):
             num_kv_heads=1,
             layer_id=layer_id,
             v_head_dim=self.kv_lora_rank,
+            quant_config=quant_config,
             prefix=add_prefix("attn_mqa", prefix),
         )
 
@@ -679,6 +681,7 @@ class DeepseekV2AttentionMLA(nn.Module):
             num_kv_heads=self.num_local_heads,
             layer_id=layer_id,
             v_head_dim=self.v_head_dim,
+            quant_config=quant_config,
             prefix=add_prefix("attn_mha", prefix),
         )