[XPU][CI] Disable test_xpu_graph until tc_piecewise is removed (#41634)

[arathi-hlab]

Motivation

XPU CI (stage-a-test-1-gpu-xpu) fails on every PR in test/registered/xpu/test_xpu_graph.py, e.g. https://github.com/sgl-project/sglang/actions/runs/37169947775/job/111340729252 (PR #40190):

torch._dynamo.exc.Unsupported: Unsupported object.__new__ user-defined class construction
  class=<class 'sglang.srt.layers.layer_boundary.residual.stream.Contribution'>,
  error=object.__new__(Contribution) is not safe, use Contribution.__new__()

The test runs Qwen2.5-1.5B with the tc_piecewise prefill graph, which compiles the decoder with fullgraph=True. Since #42301 the Qwen2 forward builds layer-boundary values that are msgspec.Structs, and Dynamo (torch 2.13) cannot construct a msgspec.Struct inside a compiled region.

Modifications

Per @mingfeima's review (#42524 (comment)): tc_piecewise is being removed in #41634, so this PR no longer reworks the layer-boundary classes. It only marks test_xpu_graph.py as disabled= in its register_xpu_ci(...) call, with a reason pointing at #41634, so run_suite.py skips the file (same mechanism as test/registered/xpu/test_triton_attention_backend.py). The XPU graph test will be refactored once #41634 lands.

The earlier version of this PR (plain __slots__ classes for the per-forward layer-boundary values, rebased from #41845) is dropped.

Verification

• pre-commit run --files test/registered/xpu/test_xpu_graph.py passes.
• The AST registry parser (ut_parse_one_file) returns the file with disabled= set, so run_suite.py --hw xpu lists it under skipped tests instead of running it.
• XPU CI stage-a-test-1-gpu-xpu should be green on this PR.

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CI States

Latest PR Test (Base): ⏳ Run #37253885968
Latest PR Test (Extra): ⚠️ Not enabled -- add run-ci-extra label to opt in.
Latest PR Test (AMD ROCm 10): ⏳ Run #37253886036

[mingfeima]

sglang is dropping tc_piecewise graph #41634. I recommend just disable the failed xpu test case in ci right now, and refactor once the above PR landed.

no need to fix upon existing tc piecewise any more.