fix: enable XPU support and update hardcoded CUDA selections for tests (#7401)

* fix: add XPU device support and update hardcoded CUDA selections

* fix: add XPU device support for pytest CUDA skipped tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix device handling for PR #7401

- perplexity_eval.py: use DEVICE_TYPE_TORCH, not DEVICE_TYPE. The latter can
  be "hip" or "mlx", which .to() rejects, so this regressed ROCm.
- test_batched_leftpad_generation_gpu.py: XPU diverges here today, so mark it
  non-strict xfail on XPU instead of reverting to a CUDA-only guard. Keeps the
  real XPU gap visible and turns green once it is fixed.
- Guard torch.xpu.is_available() with hasattr, matching device_type.py.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Re-enable the flash varlen attention test in CI for PR #7401

attention_dispatch.py now predefines flash_attn_func / flash_attn_varlen_func
as None, so test_run_attention_flash_varlen_receives_window_and_softcap no
longer needs flash_attn importable to be monkeypatched. Verified on a runner
shaped like the CPU-only one: the test fails against main's attention_dispatch
and passes at this head, so the deselect is now dead weight.

* Tighten comments for PR #7401

Drop the hasattr rationale: torch.xpu has existed since torch 2.3 and the
dependency floor is 2.4, so no supported build predates the namespace. The
guard stays as cheap defence, but the comment claimed something untrue.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: danielhanchen <danielhanchen@gmail.com>

.github/workflows/consolidated-tests-ci.yml

@@ -372,12 +372,10 @@ jobs:
             tests/python/test_fast_language_model_text_only.py \
             tests/test_bad_mappings_redirect.py \
             tests/test_prefetch_snapshot_scope.py \
-            tests/test_gemma_2b_mapper_key.py \
-            --deselect 'tests/utils/test_attention_masks.py::test_run_attention_flash_varlen_receives_window_and_softcap'
-          # The deselected test monkeypatches flash_attn_varlen_func, which is
-          # only bound on the module when `flash_attn` is importable. flash_attn
-          # requires CUDA + dev toolchain, which the CPU-only ubuntu-latest
-          # runner does not have. The other Bucket-A tests pass cleanly.
+            tests/test_gemma_2b_mapper_key.py
+          # test_run_attention_flash_varlen_receives_window_and_softcap was deselected
+          # until attention_dispatch.py predefined flash_attn_varlen_func as None; it
+          # monkeypatches that name, so it no longer needs flash_attn on this runner.
 
       - name: unsloth_zoo @ ${{ env.UNSLOTH_ZOO_REF }} — full pytest (CPU)
         # 106 of 111 test_* in unsloth_zoo are CPU-only. The two CUDA-skip