[Feature]Support ragged prefill in flashinfer mla backend (#3967)

Co-authored-by: Yineng Zhang <me@zhyncs.com>
Co-authored-by: pankajroark <pankajroark@users.noreply.github.com>

python/sglang/srt/models/deepseek_v2.py

@@ -520,10 +520,11 @@ class DeepseekV2AttentionMLA(nn.Module):
 
         def no_absorb() -> bool:
             if global_server_args_dict["enable_flashinfer_mla"]:
-                # Flashinfer MLA: Only do not use absorb when prefilling/extending without radix cache
+                # Flashinfer MLA: Do not absorb when enabling ragged prefill
                 return (
-                    global_server_args_dict["disable_radix_cache"]
+                    not global_server_args_dict["flashinfer_mla_disable_ragged"]
                     and forward_batch.forward_mode.is_extend()
+                    and forward_batch.extend_prefix_lens.sum() == 0
                 )
             else:
                 # Triton: Use normal computation for prefill and use weight absorption for extend/decode