Layout-only C ABI contract for the EdgeFirst tensor surface.
Plain #[repr(C)] values and the integer vocabularies, declared exactly
once. Every -capi crate imports these instead of carrying an "identical
copy" — r2's duplication was safe but unverified-by-construction; a single
declaration makes divergence impossible instead of merely absent.
This crate has no dependencies and must never gain one. The vocabulary
values are asserted against edgefirst-tensor's authority from the crates
that depend on both (see edgefirst-tensor-capi/src/codes.rs) — this
crate is emitted surface, never a second authority.