v0.2.1

• Reuse the Huffman tree during depth selection. Optimal-depth trials
  restore leaf lengths from the original internal nodes instead of sorting
  and rebuilding the same tree for each depth. Table selection and encoded
  bytes remain identical to zstd 1.5.7.

• Less work on incompressible blocks. After a failed Huffman attempt,
  raw literals that already exceed the block's compression threshold cause
  an early raw-block decision. This avoids copying a literals section and
  encoding sequences that would be discarded. Short output buffers retain
  their existing error behavior, and frames remain byte-identical to C.

• Simpler fast/dfast candidate checks. Bounded reads from the searchable
  history reject stale indices and guard the comparison word with one range
  check. The search order and minimum-match specializations are unchanged.

• Wider match comparisons. Fast, double-fast and lazy search share a
  word-first, 128-byte scan in the selected SIMD backend. On AVX2 it tests
  four vectors together, then resolves the first differing word. Short
  matches and bounded tails keep their exact bytewise semantics.

• Less output initialization in cold compression. compress and
  compress_into reserve the same capacity but initialize the output of
  inputs larger than 128 KiB one block at a time, reusing unwritten room.
  The RLE check uses bulk slice comparison. Frames remain byte-identical
  to zstd 1.5.7; caller-owned slices keep their exact capacity semantics.

• Faster empty and tiny inputs at levels 11-22. The optimal parser's
  position and match tables are sized per block on first use
  (min(block + 3, ZSTD_OPT_SIZE) entries) instead of being filled to
  4099 entries at every frame start. Frames are unchanged.

• Updated compression benchmarks
  for the final working tree: 384 measurements, median speed relative to C
  1.000×, with lower mean latency in 96 of 192 dataset/level pairs. All
  frames remain byte-identical to zstd 1.5.7. Large text remains slower;
  the aggregate does not establish an overall lead.

• Faster Decompressor::decompress and decompress_into. Raw and RLE
  blocks are appended in one pass instead of zeroing room and copying over
  it; frames that declare a content size are decoded into a vector cut at
  their end, so neither slack nor spare capacity is kept (a declared frame's
  vector now has exactly its length as capacity); capacity doubles, bounded
  by the frame, and a declared size is reserved up front up to 32 bytes per
  unread input byte. 1 MiB of random data decodes in 20.1 µs (was 43.8 µs;
  zstd 1.5.7 20.6 µs), 64 KiB in 1.01 µs (was 1.82 µs; zstd 1.79 µs). Errors
  are unchanged: a frame that overruns its declared size is re-decoded uncut
  to report the same ContentSizeMismatch.

• New cold comparison against zstd 1.5.7 in benchmarks/comparison
  (its own workspace): mbrotli's eight datasets, including Alice in
  Wonderland (testdata/alice29.txt), at levels -5, -1 and 1-22, with
  byte-identity preflight, CSV export, and generated per-level pages,
  per-dataset charts and run reports in docs/benchmarks/, laid out as
  mbrotli's benchmark documentation. See docs/benchmarking.md.