Move buffered-input presence, offset subtraction, and block-size validation into
Rust while keeping the private MT progression query behind its C callback. The
C entry point now projects only the consumed/produced counters, input-buffer
fields, and worker dispatch inputs. Rust preserves the null-buffer behavior and
aborts on the same impossible offset or oversized-buffer invariants as the
original C assertions.
Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo check --manifest-path rust/Cargo.toml --tests
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1
ddidderr
42e6662a6d