Drop Python 3.9 support (EOL)

- Update `requires-python` to `>=3.10`
- Remove 3.9 from test matrix and classifiers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ryan-williams

.github/workflows/tests.yaml

@@ -53,20 +53,8 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest]
-        pyv: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+        pyv: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         include:
-        - os: windows-latest
-          pyv: "3.9"
-          pytestargs: "--splitting-algorithm=least_duration --splits 4 --group 1"
-        - os: windows-latest
-          pyv: "3.9"
-          pytestargs: "--splitting-algorithm=least_duration --splits 4 --group 2"
-        - os: windows-latest
-          pyv: "3.9"
-          pytestargs: "--splitting-algorithm=least_duration --splits 4 --group 3"
-        - os: windows-latest
-          pyv: "3.9"
-          pytestargs: "--splitting-algorithm=least_duration --splits 4 --group 4"
         - os: windows-latest
           pyv: "3.10"
           pytestargs: "--splitting-algorithm=least_duration --splits 4 --group 1"

pyproject.toml

@@ -16,11 +16,10 @@ license = "Apache-2.0"
 license-files = ["LICENSE"]
 authors = [{ name = "Dmitry Petrov", email = "dmitry@dvc.org" }]
 maintainers = [{ name = "Ryan Williams" }]
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 classifiers = [
     "Development Status :: 4 - Beta",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",