Optimize deployment time for Kamal workflow

[adrienpoly]

We have a GitHub workflow that runs tests and, upon success, deploys the main branch using Kamal.

The deployment process takes about 5 minutes with a warm cache but can extend to 25 minutes with a cold cache (e.g., when gems or the Ruby version need updating).

While this delay might be an inherent limitation of GitHub runners, I’d like to explore ways to optimize the deployment time and improve overall performance.

[adrienpoly]

maybe this could help down the road https://github.com/basecamp/kamal/pull/885/files