align: Match upstream Python version support (3.9-3.13)

- Remove Python 3.7, 3.8 from classifiers and tox.ini
- Align with upstream MongoEngine's current support matrix
- Upstream only tests Python 3.9+ in their CI/tox configuration
- Keep python_requires='>=3.7' for backward compatibility

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: jeonghanjoo

setup.py

@@ -33,8 +33,6 @@ def get_version(version_tuple):
     "Operating System :: OS Independent",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",
-    "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",

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 envlist =
     pypy3-{mg3123,mg3130,mg402,mg433,mg441,mg462,mg473,mg480,mg492,mg4101,mg4112,mg4130}
-    py{37,38,39,310,311,312,313}-{mg3123,mg3130,mg402,mg433,mg441,mg462,mg473,mg480,mg492,mg4101,mg4112,mg4130}
+    py{39,310,311,312,313}-{mg3123,mg3130,mg402,mg433,mg441,mg462,mg473,mg480,mg492,mg4101,mg4112,mg4130}
 skipsdist = True
 
 [testenv]