feat: support custom client config signing with self-owned Ed25519 key - #2

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions-rs/cargo@844f36862e911db73fe0815f00a4a2602c279505, actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5, actions/github-script@d7906e4ad0b1822421a7e6a35d5ca353c962f410. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/