support py313 and drop py38 and py37

[shenxianpeng]

Change Summary

• Added support for Python 3.13
• Dropped support for Python 3.7 and 3.8
• Removed usage of the deprecated imghdr module
• Replaced pkg_resources, which was removed in Python 3.13

---

This patch fixes the following issues and pull request from the original repository:

• Replaced depreciated pkg_resources with importlib.resources in precalculated_text_measurer.py for Python 3.12 support google/pybadges#45
• imghdr removal google/pybadges#47
• pkg_resources is not available by default in Python 3.12 google/pybadges#44

[Copilot]

Pull Request Overview

This PR adds Python 3.13 support, removes legacy Python 3.7/3.8 compatibility, and migrates resource loading and image type detection to modern stdlib APIs and the filetype library.

• Update setup.py to require ≥3.9, drop old classifiers, add filetype dependency, and include Python 3.13 classifier
• Replace pkg_resources with importlib.resources in resource-loading modules and add error handling
• Refresh development tooling: bump Pillow in noxfile.py, update build_golden_images.py, and add a Python 3.13 job in CI

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
setup.py	Drop Py 3.7/3.8 support, require ≥3.9, add Python 3.13 classifier and filetype dependency
pybadges/precalculated_text_measurer.py	Swap pkg_resources for importlib.resources, handle .xz/.json assets, catch errors
pybadges/init.py	Replace imghdr usage with filetype.guess()
noxfile.py	Bump Pillow to 11.2.1 for new Python versions
build_golden_images.py	Use importlib.resources.as_file() for test data and golden images
.github/workflows/ci.yml	Add a compatibility job for Python 3.13

Comments suppressed due to low confidence (2)

pybadges/precalculated_text_measurer.py:78

• Add unit tests to exercise both the .xz and .json resource-loading branches to verify fallback behavior.

if importlib.resources.is_resource(__package__, 'default-widths.json.xz'):

build_golden_images.py:49

• [nitpick] For clearer intent and reliability, import the tests module and pass it to importlib.resources.files() instead of a string literal.

with importlib.resources.as_file(importlib.resources.files('tests') / 'test-badges.json') as test_badges_path: