Break generated exec code into subpackages?

Is it possible to break the code generated by the `exec` section of the config into subpackages?

Motivation: I have a fairly large project and the generated `exec` code is about 1 million lines of code. Since all this code is in one package, any change, even a tiny one like fixing a typo, requires recompiling the whole package which can take a few minutes, which really slows down development. Breaking the code into subpackages would allow for partial build-caching of the `generated` package and improve build times in development.

I've found other related issues, for example #1265, that talk about splitting the generated `exec` code into separate files, but not into separate packages.

[Ent](https://github.com/ent/ent) does something like this by putting each model in its own package within the `ent` package so that changes to a single model minimize recompiling (their motivation may have been different, but that is a benefit).