Add Mistral Small 4 (Pixtral) support (#20708)

Signed-off-by: Xinyuan Tong <xinyuantong.cs@gmail.com>
Co-authored-by: Alex Nails <alexnails@radixark.ai>
Co-authored-by: Dimitrios Bariamis <12195802+dbari@users.noreply.github.com>
Co-authored-by: dbari <dbari@users.noreply.github.com>

python/sglang/srt/models/deepseek_v2.py

@@ -1216,8 +1216,11 @@ class DeepseekV2AttentionMLA(
                 device=get_global_server_args().device,
             )
 
-            if rope_scaling:
-                self.scaling = compute_mla_mscale_scaling(rope_scaling, self.scaling)
+            if rope_scaling and rope_scaling.get("apply_yarn_scaling", True):
+                mscale_all_dim = rope_scaling.get("mscale_all_dim", False)
+                scaling_factor = rope_scaling["factor"]
+                mscale = yarn_get_mscale(scaling_factor, float(mscale_all_dim))
+                self.scaling = self.scaling * mscale * mscale
         else:
             self.rotary_emb = None
         self.use_deepseek_yarn_rope = rope_scaling is not None