ci(interop-tests): verify generated Go FFI binding freshness

[coderabbitai]

Summary

Add a CI freshness check for the committed Go FFI binding at interop-tests/src/tests/go_app/ffi_gen.go.

Required changes

Add a CI step that enables the existing rust2go::RegenArgs configuration in interop-tests/build.rs, regenerates ffi_gen.go, and fails when the generated file differs from the committed version. Keep the normal build configuration unchanged so ordinary test builds do not regenerate the binding.

Rationale

ffi_gen.go is tracked in Git and used by the Go interop tests. The current CI configuration lints the directory but does not verify that ffi_gen.go is synchronized with interop-tests/src/tests/go_ffi.rs. A freshness check prevents stale generated bindings from being merged.

Affected areas

• interop-tests/build.rs
• interop-tests/src/tests/go_ffi.rs
• interop-tests/src/tests/go_app/ffi_gen.go
• CI workflow or script that runs interop-test checks

Acceptance criteria

• CI has a dedicated check that regenerates ffi_gen.go using the existing rust2go::RegenArgs source and destination.
• The check fails if regeneration changes interop-tests/src/tests/go_app/ffi_gen.go.
• Normal builds and test runs continue to avoid automatic Go FFI regeneration.
• The check documents or makes clear how it enables regeneration only for validation.

Backlinks

• Pull request: fix(build): wasteful go ffi tests rebuild #7466
• Review comment: fix(build): wasteful go ffi tests rebuild #7466 (comment)
• Requested by: @LesnyRumcajs

[LesnyRumcajs]

I know one Go expert that would love to take this. @EclesioMeloJunior