feat(rust): port Huffman decompression

Move Huffman decoding-table construction and X1/X2 single- and four-stream
decoding into Rust. The original C translation unit is now a declaration shim,
so unchanged C callers and tests resolve the public decoder ABI from the Rust
archive.

The portable implementation preserves the C workspace and error contracts,
retains the existing assembly-only internal fast loops, and mirrors the C
32-bit decode cadence so X2 writes remain within its required output window.
Forced X1/X2 modes follow the matching archive configuration from the build
integration.

Test Plan:
- cargo clippy; cargo clippy --benches; cargo clippy --tests
- cargo +nightly fmt, then repeat the Clippy checks
- cargo test --all-targets for default, forced X1, and forced X2 modes
- cargo build and cargo test for i686-unknown-linux-gnu in all three modes
- Strict normal, X1, and X2 C shim compilation
- Original fuzzer and fullbench compatibility targets

Refs: rust/README.md
Depends-on: d89ebb31

rust/src/lib.rs

@@ -10,6 +10,7 @@ pub mod errors;
 pub mod fse_compress;
 pub mod fse_decompress;
 pub mod hist;
+pub mod huf_decompress;
 pub mod mem;
 pub mod pool;
 pub mod threading;