add pkg_resources import handler

[tw-yshuang]

Summary

• Replace deprecated pkg_resources with importlib.metadata for version detection
• Add fallback to pkg_resources for compatibility with older Python/setuptools versions
• Fixes compatibility issues with setuptools >= 82.0.0 where pkg_resources is deprecated

Changes

The code now:

1. First attempts to use importlib.metadata.version() (standard in Python 3.8+)
2. Falls back to pkg_resources.get_distribution() if importlib.metadata is unavailable
3. Handles PackageNotFoundError/DistributionNotFound for development environments

Testing

Verified on setuptools 82.0.0 - version detection works correctly.