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

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

python/sglang/srt/models/gemma3_causal.py

@@ -193,6 +193,7 @@ class Gemma3Attention(nn.Module):
             # Module must also define `get_attention_sliding_window_size` to correctly initialize
             # attention backend in `ForwardBatch`.
             sliding_window_size=self.sliding_window,
+            quant_config=quant_config,
             prefix=add_prefix("attn", prefix),
         )