Move the high-level ZSTDMT compression-job stage sequence into Rust: resource
acquisition, per-job parameter preparation, serial sequence handling, context
initialization, external-sequence application, non-first frame-header repair,
chunk compression/error routing, tracing, and common finalization. Keep C-owned
job descriptors, pools, synchronization, codec contexts, serial state, and
cleanup behind callbacks so private worker state does not cross the boundary.
Test Plan:
- Rust library all-target tests: 517 passed, including MT job-order tests.
- Rust legacy feature matrix: 572 passed.
- Rust and CLI clippy, nightly fmt, native CLI tests (41), and library smoke.
- Native test-zstd, bounded fuzzer (319), zstream (152 + 297), and decode
corpus (1,647) all passed, including multi-GiB and MT round trips.
- All heavy checks ran serially with CARGO_BUILD_JOBS=1 or make -j1 and
ulimit -v 41943040 (40 GiB virtual memory).
- Commit is intentionally unsigned because configured GPG pinentry was
unavailable and hung during the signing attempt.