ZSTDMT_nextInputSizeHint only derives a size_t hint from targetSectionSize
and inBuff.filled. Keep the MT context, public/internal entry point, and
stream orchestration in C, but delegate those two scalars to Rust. The Rust
helper uses wrapping subtraction and preserves the zero-result fallback,
including C's wrapped behavior for invalid overfill.
Test Plan:
- The three compression clippy modes passed before and after
`cargo +nightly fmt --manifest-path rust/Cargo.toml`.
- Focused Rust tests passed: 5 `mt_next_input_size_hint` tests.
- `make -B -C lib -j2 lib` passed.
- `make -C tests test-rust-lib-smoke` passed.
- `tests/fuzzer -s4560 -t56 -i57 -v` passed: 57 tests completed.
- `make -C tests -j2 test-zstream` passed: 84 named, 6,659, and 8,055
randomized tests completed.
- `git diff --check` and `git diff --cached --check` passed.
ddidderr
564c82e70f