Add Python 3.15 classifier

Author: ifduyue

setup.py

@@ -53,6 +53,7 @@
         "Programming Language :: Python :: 3.12",
         "Programming Language :: Python :: 3.13",
         "Programming Language :: Python :: 3.14",
+        "Programming Language :: Python :: 3.15",
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Free Threading :: 1 - Unstable",
     ],