Update Python version requirement to >=3.8

- Update pyproject.toml requires-python from >=3.6 to >=3.8
- Update setup.cfg classifiers to remove Python 3.6 and 3.7 support
- Add support for Python 3.8, 3.9, 3.10, 3.11, and 3.12
- Update Dockerfile.dev to use Python 3.8 base image

This change is necessary because the code uses importlib.metadata
which was introduced in Python 3.8, making the previous >=3.6
requirement incorrect and causing import errors on older versions.

Author: sunnywu

pyproject.toml

@@ -18,7 +18,7 @@ classifiers = [
     "License :: OSI Approved :: MIT License",
     "Operating System :: OS Independent",
 ]
-requires-python = ">=3.6"
+requires-python = ">=3.8"
 dependencies = [
     "setuptools",
     "pycryptodome",

setup.cfg

@@ -15,10 +15,11 @@ classifiers =
     Natural Language :: English
     Operating System :: OS Independent
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     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
     Topic :: Internet
     Topic :: Software Development :: Libraries :: Python Modules
     Topic :: Utilities