Scala CI on GitHub Actions

sbt spends longer starting up and resolving than compiling.

Why it happens

sbt boots a JVM, resolves Coursier dependencies and loads the build definition before a single file compiles.

What to change

1. Cache ~/.cache/coursier, ~/.sbt and the target/ directories
2. Use sbt --client or run all tasks in a single sbt invocation
3. Enable the Zinc incremental compiler cache across runs
4. Give the JVM 8 GB or more — Scala compilation is memory-hungry

Scala on runnerhut

jobs:
  test:
    runs-on: runnerhut-8vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4
      - uses: coursier/cache-action@v6
      - run: sbt "compile; test"

The only runnerhut-specific line is `runs-on: runnerhut-8vcpu-ubuntu-2404`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.