Remove Python 3.9 support (#47)

Author: rocky

pyproject.toml

@@ -22,7 +22,7 @@ dependencies = [
         "matplotlib",
         "scipy>=1.10.0",
 ]
-requires-python = ">=3.9" # Sympy 1.11 is supported only down to 3.8
+requires-python = ">=3.10"
 readme = "README.rst"
 license = {text = "GPL"}
 keywords = ["Mathematica", "Wolfram", "Interpreter", "Shell", "Math", "CAS"]
@@ -34,7 +34,6 @@ classifiers = [
     "Intended Audience :: Science/Research",
     "License :: OSI Approved :: GNU General Public License v3 (GPLv3)",
     "Programming Language :: Python",
-    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",