feat(rust): port sequence entropy encoding

Move FSE table-costing, table construction, encoding selection, and sequence
bitstream emission into Rust while retaining the existing C internal-header
boundary. The shim preserves all five C ABI entry points, so the surrounding
compressor continues to consume C-shaped sequence and entropy-table storage.

Test Plan:
- cargo clippy
- cargo clippy --benches
- cargo clippy --tests
- cargo +nightly fmt
- cargo test --all-targets
- cargo test --target i686-unknown-linux-gnu zstd_compress_sequences::tests
- C-vs-Rust differential across 163 payload cases on x86_64 and i686
- fuzzer, zstreamtest, and invalidDictionaries

Refs: Rust FSE compression port 5f9d607d

rust/src/lib.rs

@@ -23,6 +23,8 @@ pub mod xxhash;
 pub mod zstd_common;
 #[cfg(feature = "compression")]
 pub mod zstd_compress_literals;
+#[cfg(feature = "compression")]
+pub mod zstd_compress_sequences;
 #[cfg(feature = "decompression")]
 pub mod zstd_ddict;
 #[cfg(feature = "compression")]