ci: drop Python 3.10 and promote python.supported to ci/versions.yml (13.4.x backport) - #3085

Backport of #3080 (merged on main) to the 13.4.x maintenance branch. Not a straight git cherry-pick — the branch pre-dates several things PR 3080 touched (check_cuda_core_bindings_floor, sample_runner, pyproject/pixi restructures), so the change is re-applied by hand with the same pattern.

SSoT (backport of the cupy pattern used in #3080)

• ci/versions.yml — add a python block with supported: list. Same shape as the main-branch version.
• .github/workflows/ci.yml — expose PYTHON_SUPPORTED from the existing ci-vars job via yq -o json -I 0 '.python.supported' ci/versions.yml; thread it to every build-wheel.yml call. The baseline-reuse yq read of build-wheel.yml's matrix is retargeted to ci/versions.yml.
• .github/workflows/build-wheel.yml — add python-versions input; matrix sources it via fromJSON(inputs.python-versions). The dead win-arm64 && 3.10 exclude is removed with the matrix.

3.10 drops

• python.supported lands with 3.11 .. 3.15t only.
• ci/test-matrix.yml — delete the 9 PY_VER: '3.10' rows.
• All five pyproject.tomls — drop the 3.10 classifier and bump requires-python to >=3.11.
• cuda_bindings/pixi.toml, cuda_core/pixi.toml — drop "3.10.*" from the python feature matrix. cuda_pathfinder/pixi.toml — python = ">=3.10" → ">=3.11".
• ruff.toml — target-version = "py310" → "py311". mypy python_version pins in cuda_core/pyproject.toml and cuda_pathfinder/pyproject.toml bump to "3.11".

Cleanups unlocked by the 3.11 floor

• cuda_core/cuda/core/typing.py — collapse the StrEnum backport shim (enum.StrEnum is stdlib on 3.11+).
• cuda_core/cuda/core/_utils/pycompat.py — drop the 3.11 StrEnum shim; keep the 3.12 BufferProtocol block.
• cuda_core/pyproject.toml — drop the backports.strenum; python_version < '3.11' runtime dep.
• cuda_core/pixi.toml — drop the unconditional backports.strenum dep.
• cuda_bindings/tests/test_basics.py + cuda_core/tests/test_enum_coverage.py — drop dead sys.version_info >= (3, 11) blocks.

Drive-by ruff fixes (same as #3080)

• toolshed/check_spdx.py — datetime.timezone.utc → datetime.UTC (UP017).
• ci/tools/check_pixi_cuda_version.py — I001 import sort.

Docs

• cuda_bindings/docs/source/install.rst, support.rst — Python 3.10 - 3.14 → 3.11 - 3.15. Also drop python310 and add python315 / python315t to the nightly-wheel example.
• cuda_core/docs/source/install.rst, support.rst — same bump; add "3.14 and 3.15" to the free-threaded mention.
• cuda_pathfinder/docs/source/install.rst — same bump.

Release notes

• cuda_core/docs/source/release/1.3.0-notes.rst — add a Highlights bullet (file already exists on this branch).
• New placeholder files for the next release of each other project: cuda_bindings/docs/source/release/13.4.4-notes.rst, cuda_pathfinder/docs/source/release/1.8.2-notes.rst, cuda_python/docs/source/release/13.4.2-notes.rst.

pixi.lock refresh

Regenerated pixi.lock (root) + cuda_bindings/pixi.lock + cuda_core/pixi.lock + cuda_pathfinder/pixi.lock + benchmarks/cuda_bindings/pixi.lock + benchmarks/cuda_core/pixi.lock with pixi 0.81.0 to track the pixi.toml / pyproject.toml changes.

-- Leo's bot