Intermittent build error when changing selected features

[avantgardnerio]

Describe the bug

Now that codegen has been moved into the proto/src/datafusion.rs file, that file can have two different sets of contents depending on whether or not the json feature is selected (which some CI build & test have each way). When the feature flags are changed, the contents aren't necessarily regenerated, causing intermittent build issues.

To Reproduce

Run a regular build, then try to run the extra-long cargo check command from CI:

cargo check --workspace --benches --features avro,jit,scheduler,json

Expected behavior

Builds always work.