feat: Drop support for Python 3.8 and 3.9 (EOL)

Both Python 3.8 and 3.9 have reached end-of-life:
- Python 3.8: EOL October 7, 2024
- Python 3.9: EOL October 31, 2025

Changes:
- Add python_requires=">=3.10" to setup.py
- Remove Python 3.8 and 3.9 from classifiers
- Add Python 3.13 and 3.14 to classifiers
- Update README to document Python 3.10+ requirement

Author: Iamrodos

README.rst

@@ -9,8 +9,8 @@ The package can be used to backup an *entire* `Github <https://github.com/>`_ or
 Requirements
 ============
 
+- Python 3.10 or higher
 - GIT 1.9+
-- Python
 
 Installation
 ============

setup.py

@@ -40,15 +40,16 @@ def open_file(fname):
         "Development Status :: 5 - Production/Stable",
         "Topic :: System :: Archiving :: Backup",
         "License :: OSI Approved :: MIT License",
-        "Programming Language :: Python :: 3.8",
-        "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",
     ],
     description="backup a github user or organization",
     long_description=open_file("README.rst").read(),
     long_description_content_type="text/x-rst",
     install_requires=open_file("requirements.txt").readlines(),
+    python_requires=">=3.10",
     zip_safe=True,
 )