@delphi/common is the SvelteKit project producing the package we want to import. @delphi/common/package is the package directory (after running npm run package from @delphi/common).
In the root package, we can run npm install --save-dev ./@delphi/common/package, and the package my-test-package (the name given in @delphi/common/package.json) will be available to us in the root package as import MyComponent from 'my-test-package/MyComponent.svelte'.