Bump Python version requirement to 3.12.

[trivialfis]

CI: dmlc/xgboost-devops#88
Close #12194

After this PR, I will try to bring rapids to 26.04, and see if we can resolve the CI failure with the latest CCCL.

Changes:

• Update requirement to Python 3.12.
• Raise a warning about the changed behavior from arrow.
• Typing updates.
• Fix a race in tracker initialization.

Breaking:

• Drop pandas sparse array support for column split.

todos

• Revert image tag.

[Copilot]

Pull request overview

This PR raises XGBoost’s minimum supported Python version to 3.12 and updates related packaging, CI, docs, and a few compatibility helpers to assume newer stdlib features.

Changes:

• Bump requires-python to >=3.12 and update Python version pins across CI / conda envs / RTD.
• Remove legacy Python-3.10 compatibility branches (e.g., hashlib.file_digest gating; custom cd() workaround in PEP517 backend).
• Minor typing / behavior tweaks in Python utilities and docs configuration.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/python/test_model_compatibility.py	Assume hashlib.file_digest exists (Python 3.12+).
src/collective/tracker.cc	Move tracker ready_ flip closer to socket watch setup.
python-package/xgboost/compat.py	Add explicit cast for numpy concatenate return typing.
python-package/xgboost/_typing.py	Expand NumpyDType to include np.dtype[Any].
python-package/xgboost/_data_utils.py	Replace hard assert on embedded NUL with a warning.
python-package/pyproject.toml.stub.in	Set requires-python = ">=3.12" and drop 3.10/3.11 classifiers.
python-package/pyproject.toml.in	Set requires-python = ">=3.12" and drop 3.10/3.11 classifiers.
python-package/pyproject.toml	Set requires-python = ">=3.12" and drop 3.10/3.11 classifiers.
python-package/packager/pep517.py	Switch to contextlib.chdir (stdlib) and remove custom cd().
ops/pipeline/get-image-tag.sh	Update CI image tag selection (currently hardcoded to PR tag).
ops/pipeline/build-python-wheels-macos.sh	Build wheels using CPython 3.12.
ops/pipeline/build-python-wheels-cpu.sh	Use CPython 3.12 path in manylinux image.
ops/conda_env/win64_test.yml	Pin Python 3.12 for Windows conda tests.
ops/conda_env/sdist_test.yml	Pin Python 3.12 for sdist tests.
ops/conda_env/python_lint.yml	Pin Python 3.12 for lint env.
ops/conda_env/minimal.yml	Pin Python 3.12 for minimal env.
ops/conda_env/macos_cpu_test.yml	Pin Python 3.12 for macOS CPU tests.
ops/conda_env/linux_sycl_test.yml	Pin Python 3.12 for SYCL tests.
ops/conda_env/linux_cpu_test.yml	Pin Python 3.12 for Linux CPU tests.
ops/conda_env/aarch64_test.yml	Pin Python 3.12 for aarch64 tests.
doc/xgboost_doc.yml	Pin Python 3.12 for docs conda env.
doc/contrib/docs.rst	Update docs build instructions to Python 3.12.
doc/conf.py	Update intersphinx Python docs to 3.12; small refactors/docstrings.
demo/guide-python/external_memory.py	Small cleanups/typing/import adjustments; rename args for clarity.
.readthedocs.yaml	Set RTD build toolchain Python to 3.12.
.github/workflows/r_tests.yml	Use Python 3.12 for R workflow’s Python step.
.github/workflows/python_wheels_winarm64.yml	Use Python 3.12 for wheel build workflow.
.github/workflows/python_wheels_variants.yml	Use CPython 3.12 path in manylinux container.
.github/workflows/python_tests.yml	Run Python tests on Python 3.12.
.github/workflows/pre-commit.yml	Run pre-commit with Python 3.12.
.github/workflows/main.yml	Use CPython 3.12 path in container jobs.

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[trivialfis]

Friendly ping @RAMitchell