chore(scripts): script to build only unbuilt packages

[kuhe]

Issue

none

Description

Adds a script that builds only unbuilt packages.

Testing

make unbuilt after running clean in a random client.

Additional context

Scenario: e.g. some new clients have been added and I don't want to run a full build because I don't need every client to be up to date. Running a full client build is slow.

Checklist

• [n/a] If the PR is a feature, add integration tests (*.integ.spec.ts).
• [n/a] If you wrote E2E tests, are they resilient to concurrent I/O?
• [n/a] If adding new public functions, did you add the @public tag and enable doc generation on the package?