You can push mirror your fork back to GitHub when you deem necessary (e.g when it’s in a good shape) and create a PR to the parent repo automatically using forgejo runner script, you’d just need to make an API token. If the goal is to automate PRs. If the goal is to not use GitHub for your forks but still continue to make PRs, you can’t work around that I think. Unless there’s a way to PR a bunch of patch files perhaps?
In a game that is production ready you would be going through individual assets with the person who designed them and you’d establish when to spawn and despawn them. As designers tend to go crazy and not worry about memory at all, I tend to guide them to think about memory availability in a particular scene. Really depends on the game you’re making though