feat(rust): port compression literal blocks

Move raw, RLE, and Huffman literal-section encoding into the Rust
compatibility archive.  The surrounding C block compressor continues to pass
its existing entropy workspace and Huffman-table state through the unchanged
internal ABI.

The port preserves literal header choices, compression-gain decisions,
repeat-table transitions, and 1X/4X encoder selection.  It lets ordinary C
compression paths exercise Rust code without widening this commit into the
remaining frame compressor.

Test Plan:
- cargo clippy, cargo clippy --benches, cargo clippy --tests, and nightly fmt
- cargo test --all-targets (94 passed) and feature-only cargo checks
- native fuzzer, zstreamtest, invalidDictionaries, and CLI round trip
- compare literals and next-table bytes with pristine C on x86_64 and i686

Refs: rust/README.md compression-primitives map

rust/README.md

@@ -29,6 +29,8 @@ zstd ABI:
 - Compression primitives
   - `hist` counts byte frequencies for FSE and Huffman compression.
   - `zstd_presplit` chooses split points for full compression blocks.
+  - `zstd_compress_literals` emits raw, RLE, and Huffman literal sections
+    while preserving the compressor's Huffman-table repeat state.
 - Runtime support
   - `threading` provides platform pthread wrappers required by zstd headers.
   - `pool` implements the bounded worker pool used by multithreaded compression.