Proto files are sourced from: https://github.com/esphome/esphome/blob/main/esphome/components/api/.
Unfortunately it's quite tricky to find which api version belongs to which esphome version. Best is to look for the api version response in the src code.
Adding a new version takes a couple of steps (to be automated, some day...)
- Download proto files into src/proto/<VERSION_NUMBER>
- Update Cargo.toml to support new version feature
- Update build.rs to add the new version to the list of versions
- Update src/proto.rs to add the correct include matching the feature flag