bug: `kit b --hyperapp` can fail to build if target/ is subsequently deleted

Because of how we modify both the top-level and process-level Cargo.toml file, if you

```
kit b --hyperapp
```

then

```
rm -rf target
```

then try to build again, you'll get errors until you:
1. Edit `Cargo.toml` to remove `caller-utils` workspace
2. Edit `<process/Cargo.toml` to remove `caller-utils` dependency

kit must "just work" here, not error out