Make Settings more static

Right now, methods on the settings builder are all taking strings as inputs, and maybe strings as values. This makes it very dynamic, and allows a range of runtime errors like a setting doesn't exist, or the provided value doesn't have the right type.

Instead, we could generate methods on the settings builder for each setting:

- for bool values, they would take a bool parameter.
- for enum values, they would take a (Rust) enum parameter.

Then, the entire range of errors described by the enum SetError would disappear, and all these errors would become compile-time errors, which I think is safer and less error-prone.

This implies generating more code for these settings. We don't have thousands of them, so it shouldn't be a problem. It would be a breaking API change, too.