Remove pkg_resources dependency from CLI metadata and plugin discovery

[siddicky]

Problem

The CLI imports pkg_resources at module load time for plugin discovery and version lookup. A clean uv-managed Python 3.14 tool environment installs only declared runtime dependencies, so the CLI fails before it can render help:

$ uv tool install --python 3.14 shodan
$ shodan --help
ModuleNotFoundError: No module named 'pkg_resources'

Declaring setuptools is not durable: current releases no longer provide pkg_resources, and pinning setuptools<81 only postpones removal.

Related work

• Deprecation Warning: pkg_resources will be removed after 2025-11-30 #243 tracks the deprecation warning.
• pkg_resources is deprecated as an API. #245 is a duplicate warning report.
• Error : ModuleNotFoundError: No module named 'pkg_resources' #246 reports the hard import failure.
• Replace CLI pkg_resources lookups with importlib.metadata #248 proposes an importlib.metadata path with a pkg_resources fallback.

This issue scopes a fully pkg_resources-free implementation so the CLI also works in isolated installers such as uv.

Proposed direction

• Use stdlib importlib.metadata on Python 3.8+.
• Use the official importlib-metadata backport on older supported Python versions.
• Use the metadata API for both shodan.cli.plugins entry-point discovery and the shodan version command.
• Add a regression test proving shodan.__main__ imports and --help renders when pkg_resources is unavailable.

I am preparing a focused PR with a clean uv/Python 3.14 reproduction and full test/build evidence.