The dictionary-content orchestrator still routed the Fast hash-table fill
through a C callback even though the matching leaf already lived in Rust.
Replace that callback slot with a pointer-sized C/Rust projection containing
only the Fast leaf inputs, including a by-value copy of nextToUpdate and the
normalized CDict/full-load flags. Keep the dtlm/tfp invariant assertion in C
and retain all bridge offsets and the double-Fast callback.
A broader MatchState projection would expose private layout and adding fields
would change the established 34-word bridge. The narrow projection keeps
that ABI stable while making the Fast branch call ZSTD_rust_fillHashTable
directly.
Test Plan:
- `git diff --cached --check`
- `rustfmt --check --edition 2021 rust/src/zstd_compress_dictionary.rs` (reports only pre-existing formatting drift outside this change)
- Cargo, make, and full tests intentionally not run per task instructions.
ddidderr
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