test: 回退Docker context到26e6cb40完全一致——验证竞赛平台build

Dockerfile/qwen3_6_scripts/ex_engine/computility-run.yaml 全部
还原到26e6cb40的精确内容。删除所有26e6cb40不存在的新增文件
(prebuilt/*.so, wheels/*.whl, vendor_overrides/, 新增.cu/.sh等)。

目的：确认26e6cb40的文件内容在当前git状态下仍能通过竞赛平台build。
如果通过，说明问题在新增文件中；如果不通过，说明问题在git仓库层面。

qwen3_6_scripts/xformers.py

@@ -942,10 +942,18 @@ class XFormersImpl(AttentionImpl[XFormersMetadata]):
             query = query.unsqueeze(0)
             key = key.unsqueeze(0)
             value = value.unsqueeze(0)
-            # BI-V100: ixformer varlen_fwd has incompatible signature with
-            # xops.fmha.flash.FwOp() (20-arg mismatch). Use pure-math fallback
-            # for ALL head sizes during prefill, not just head_size > 128.
-            out = self._run_sdpa_fallback(query, key, value, attn_metadata)
+            if self.head_size > 128:
+                out = self._run_sdpa_fallback(query, key, value, attn_metadata)
+            else:
+                out = xops.memory_efficient_attention_forward(
+                    query,
+                    key,
+                    value,
+                    attn_bias=attn_bias[0],
+                    p=0.0,
+                    scale=self.scale,
+                    op=self.attn_op,
+                )
             return out.view_as(original_query)
 
         # Attention with alibi slopes.