This makes code more readale and concise,
moving all format arguments like `format!("{}", foo)`
into the more compact `format!("{foo}")` form.
The change was automatically created with, so there are far less change
of an accidental typo.
```
cargo clippy --fix -- -A clippy::all -W clippy::uninlined_format_args
```
* Keep codegen adjacent to the relevant crates.
* Remove codgen deps from xtask, speeding-up from-source installation.
This regresses the release process a bit, as it now needs to run the
tests (and, by extension, compile the code).
