Fix compilation with ctk133.

[trivialfis]

close #12229
close #12225

[Copilot]

Pull request overview

This PR fixes CUDA Toolkit 13.3 compilation issues in the categorical ordinal encoder by avoiding problematic type deduction patterns seen with newer NVCC/CCCL toolchains.

Changes:

• Introduce a SegIdxT alias in detail::ColumnsViewImpl and use it for feature_segments’ element type.
• Replace a decltype(new_enc.feature_segments)::value_type host-side vector declaration with the new stable alias (decltype(new_enc)::SegIdxT) in the missing-category reporting path.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/encoder/ordinal.h	Adds SegIdxT alias and uses it to type feature_segments consistently.
src/encoder/ordinal.cuh	Uses SegIdxT for the host mirror of feature_segments, avoiding NVCC template/type deduction failures.

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[trivialfis]

[9](https://github.com/dmlc/xgboost/actions/runs/26936251008/job/79469112940?pr=12232#step:7:680)
Fatal Python error: Bus error

Current thread 0x0000edd5190fa9c0 (most recent call first):
  File "/opt/miniforge/envs/gpu_test/lib/python3.12/site-packages/xgboost/core.py", line 2203 in update
  File "/opt/miniforge/envs/gpu_test/lib/python3.12/site-packages/xgboost/training.py", line 200 in train

that's new.