Shut down workers on idle instead of a static maximum lifetime — Closes #100 - #101

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5, Swatinem/rust-cache@f0deed1e0edfc6a9be95417288c0e1099b1eeec3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/