Move ZSTD_initCStream's public initialization policy into the Rust
projection. Rust now preserves the reset, CDict-clear, and compression-level
ordering while C retains the private context callbacks and ABI boundary.
Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml init_cstream -- --test-threads=1
- ulimit -v 41943040; make -B -C programs -j1 zstd
- git diff --cached --check
ddidderr
3798dfd82c