refactor(decompress): move stack heap-mode policy to Rust
Move only the heap-mode branch decision for stack decompression into Rust
while retaining the C-owned stack context, static initialization, error codes,
and decoder projection. The Rust scalar policy preserves the historical
heapmode >= 1 rejection boundary.
Test Plan:
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings` -- passed
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 ./tests/rustLibSmoke` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1 -C tests test` -- passed, including large streaming, native, fuzzer, and zstream phases
ddidderr
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