Add Python 3.15 to the CI matrix, release workflow and classifiers

Validated against CPython 3.15.0: the full pytest suite gives the same
result as on 3.14.7 (2396 passed, 174 skipped, 924 deselected), and the
sdist/wheel build passes twine check --strict and installs cleanly into
a fresh 3.15 environment.

Author: Iris Coding Agent

.github/workflows/ci.yaml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.15"]
     steps:
       - uses: actions/checkout@v7
         with:

.github/workflows/pypi-release.yaml

@@ -16,7 +16,7 @@ jobs:
       - name: Install uv
         uses: astral-sh/setup-uv@v10.2.0
         with:
-          python-version: "3.12"
+          python-version: "3.15"
       - name: Build tarball and wheels
         run: |
           git clean -xdf

pyproject.toml

@@ -27,6 +27,7 @@ classifiers = [
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
     "Topic :: Scientific/Engineering",
     "Topic :: Software Development :: Libraries",
 ]