refactor: include new cool repo mechanisms

[AngryMaciek]

Include some new cool GitHub repo mechanisms I have learned recently:

• refactor ci: installation test as 1 job? dev env?
• .gitattributes w/ langauges, .gitignore refactor
• flake8 / lintr check
• codefactor check + shield
• dev env: YAML or requirements.TXT? conda is needed anyway...
• Makefile: dry integration tests, lint, build envs,
• Dockerfile run/dev
• DevPod configuration
• Changelog + update workflow
• linting CI
• new issue/PR templates
• codespaces configuration
• black, stylr, isort tests?
• PR workflows: size labels, title check, auto assign
• Contributing: better instructions, specific rules, more tests
• version file + autotag ci
• twitter shield
• stale pr ci
• contributor covenant shield?