Modernize packaging, fix parsing issues, and add CI

[jonasjancarik]

Summary

This PR modernizes the packaging and fixes multiple issues with the parsing logic.

Changes

Parsing Improvements

• Use JSON output format for docker ps (--format '{{json .}}') to eliminate brittle column splitting. Fixes issues where container names were misidentified when commands contained newlines or multiple spaces.
• Fix health status parsing in _parse_ps_date to correctly handle (health: starting) and other health status variants.

Packaging Modernization

• Switch to console_scripts entry point instead of scripts= to ensure proper wrapper generation on all platforms.
• Add dockerprettyps/__main__.py to support python -m dockerprettyps.
• Update shebang to #!/usr/bin/env python3.
• Escape ASCII art backslashes to fix SyntaxWarning in Python 3.12+.

CI/CD

• Add GitHub Actions workflow to test installation via pip and uv on Ubuntu, macOS, and Windows.

Documentation

• Update README to recommend modern install methods (uv tool install, pip install .).

Fixes

• Fixes Executable points to python3.7 #21 (hardcoded python3.7 shebang)
• Likely fixes/avoids pkg_resource is deprecated as API #37 (pkg_resources launcher deprecation warning)