feat: code conventions

[nandordudas]

It contain all pr's commits.

There are some interesting things you should check before doing anything. It depends on previous pr's.

• ESLint added and configured,
• code is formatted by ESLint rules,
• GitHub workflow files added, so they can be used in branch rules as requirement,
• tsup bundler added and configured,
• package.json has been updated with necessary properties to publish the package,
• add devcontainer and GitHub codespace support.

Please check scripts property in package.json file.

That's all.