ci: Gather and report test coverage in test workflow

ci: Add clean on re-run to lint workflow

ci: Cache _build directory and compile separately

ci: Update lint workflow's checkout action

ci: Set MIX_ENV to test in lint workflow

ci: Show all priorities when running Credo on CI

ci: Upgrade to actions/cache@v4

ci: Cache Bumblebee model files

ci: Install ffmpeg

ci: Use pgvector-provided image for Postgres

ci: Configure test environment for Postgres on CI

ci: Create separate `test` workflow that uses Postgres

ci: Run tests in GitHub actions workflow

ci: Fix misspelling in cache action name

ci: Define version for `setup-beam` action

ci: Check formatting and code style on GitHub Actions