Update pyproject.toml for Python 3.14

- Update version classifiers.
- Bump requires-python to 3.10.

Author: khaeru

pyproject.toml

@@ -20,16 +20,16 @@ classifiers = [
   "Operating System :: OS Independent",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
   "Programming Language :: Python :: 3.13",
+  "Programming Language :: Python :: 3.14",
   "Programming Language :: R",
   "Topic :: Scientific/Engineering",
   "Topic :: Scientific/Engineering :: Information Analysis",
 ]
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 dependencies = [
   "click",
   "ixmp >= 3.11",