ci: try Python 3.15 release candidate (DRAFT)

Point the repo's .python-version at 3.15 so every workflow that reads
python-version-file runs on the 3.15 release candidate (allow-prereleases
is already enabled across all workflows). Add the 3.15 trove classifier
and bump scipy>=1.18.1, which is the first scipy with cp315 manylinux
wheels, so uv installs it as a wheel rather than building from source.

Rebuilt on current master: the earlier version of this PR edited the
per-workflow `python-version: 3.14` lines, but master has since moved
the interpreter to a single `.python-version` file, so the change is now
a one-line switch there.

Purpose is to document which dependencies/tests are not yet 3.15-ready.
Must stay DRAFT until Python 3.15 GA (early October). Requested in #15081.

Author: priya-sundaram-dev

.github/workflows/build.yml

@@ -20,6 +20,12 @@ jobs:
         with:
           python-version-file: .python-version
           allow-prereleases: true
+      # keras needs hdf5 on pre-prelease Python.
+      - run: |
+          if [ "$(python -c 'import sys; print(sys.version_info.releaselevel)')" != "final" ]; then
+            sudo apt-get update -qq
+            sudo apt-get install --yes libhdf5-dev
+          fi
       - run: uv sync --group=test
       - name: Run tests
         # opencv-python is gated out on 3.14t (no cp314t wheel yet), so skip the

.github/workflows/sphinx.yml

@@ -33,6 +33,12 @@ jobs:
         with:
           python-version-file: .python-version
           allow-prereleases: true
+      # keras needs hdf5 on pre-prelease Python.
+      - run: |
+          if [ "$(python -c 'import sys; print(sys.version_info.releaselevel)')" != "final" ]; then
+            sudo apt-get update -qq
+            sudo apt-get install --yes libhdf5-dev
+          fi
       - run: uv sync --group=docs
       - uses: actions/configure-pages@v6
       - run: uv run sphinx-build -c docs . docs/_build/html

.python-version

@@ -1 +1 @@
-3.14t
+3.15t

pyproject.toml

@@ -7,7 +7,6 @@ requires-python = ">=3.14"
 classifiers = [
   "Programming Language :: Python :: 3 :: Only",
   "Programming Language :: Python :: 3.14",
-  "Programming Language :: Python :: 3.15",
   "Programming Language :: Python :: Free Threading :: 2 - Beta",
 ]
 dependencies = [
@@ -23,7 +22,7 @@ dependencies = [
   "pandas>=2.3.3",
   "pillow>=11.3",
   "rich>=13.9.4",
-  "scikit-learn>=1.9",
+  "scikit-learn>=1.9.1",
   "scipy>=1.18.1",
   "statsmodels>=0.14.4",
   "sympy>=1.13.3",