Fix decorators + lint script

This MR uses "poor man's decorators" as the decorators have to be used only on class methods.

When modifying the shared/helpers file, I noticed that the file was not linted. It appears that the linter does not follow well the symlinks (see https://github.com/eslint/eslint/issues/13615 and https://github.com/eslint/eslint/issues/13551), so I fixed the script to include shared and fixed the linting errors.