v0.2.4

• Dictionaries. mzstd::dictionary reads raw-content and
  Zstandard-format dictionaries (DictionaryContent::{Auto, Raw, Zstd}).
  DictionaryBuilder prepares a PreparedDictionary for one
  EncoderConfig, and Compressor gains compress_with_dictionary,
  compress_with_dictionary_into, _to_slice, _to_uninit,
  start_with_dictionary, into_session_with_dictionary and, with std,
  writer_with_dictionary and reader_with_dictionary; a dictionary
  prepared for another configuration (frame options aside) is
  EncodeError::DictionaryMismatch. Frames are byte-identical to zstd
  1.5.7's ZSTD_compress2 and ZSTD_compressStream2 after
  ZSTD_CCtx_loadDictionary_advanced: the dictionary's own tables and
  parameters (tagged fast/dfast tables), the reference's choice between
  attaching the dictionary and copying its tables, dictMatchState variants
  of every match finder (fast, dfast, greedy/lazy/lazy2 with hash chains and
  rows, btlazy2, btopt, btultra, btultra2), the dictionary's entropy tables,
  repeat offsets and ID, and the optimal parser's first-block statistics
  seeded from them. One exception, found by fuzzing: with a dictionary whose
  literal or match length table omits its last symbols, the reference's
  optimal parser reads uninitialized memory and its frames vary from run to
  run; mzstd's stay deterministic.

• Dictionary decoding. DecodeDictionary parses dictionaries as
  zstd 1.5.7's ZSTD_DDict does, rejected exactly when the reference
  rejects them; a PreparedDictionary decodes too, through
  DictionaryRef::Prepared, without a second copy of its bytes.
  Decompressor gains decompress_with_dictionary, _into, _to_slice,
  start_with_dictionary, into_session_with_dictionary and, with std,
  reader_with_dictionary/writer_with_dictionary. A frame naming another
  dictionary ID fails with the new DecodeError::DictionaryMismatch
  (DictionaryUnsupported still reports one decoded without a dictionary).
  EncoderSessionOwned and DecoderSessionOwned gain a defaulted type
  parameter for the dictionary they own. Decoding without a dictionary is
  unchanged.

• Parallel segments are primed with the input before them instead of
  compressing it. For fast, dfast, greedy, btopt, btultra and btultra2,
  each segment loads its overlap as a raw-content prefix, the way ZSTDMT
  primes a job (ZSTD_compressBegin_advanced_internal with
  ZSTD_dtlm_fast and forceWindow; checked byte-identical against
  ZSTD_CCtx_refPrefix with ZSTD_c_forceMaxWindow at every level, LDM
  included), where the overlap used to be compressed and thrown away.
  Lazy, lazy2 and btlazy2 still compress it: loading made them up to three
  times slower on random input (lazy, lazy2) and 9% slower on text
  (btlazy2). Overlap sizes are unchanged. With four threads and 4 MiB
  segments on 16 MiB of text, binary, random and mixed data and on the
  vendored zstd sources (i7-13700KF, benches/parallel.rs
parallel-corpora, new): levels 18-22 run 15-27% faster (binary level
  19: 2.34 s instead of 2.77 s) with frames 0.01-0.27% larger, levels 1-5
  up to 27% faster and levels 16-17 1-7% faster with frames within 0.12%;
  levels 6-15 are unchanged. Parallel output changes; serial output does
  not. Each stream segment's buffer is now allocated once at its full size,
  and batch assembly reserves the frame.

• Cheaper Huffman code packing. Literals packed their codes symbol by
  symbol with a branch; the packing is now branch-free over the whole
  alphabet in the backend's feature context, which matters for a
  dictionary's 256-symbol table (one 107-byte record with a dictionary: 9.2k
  instructions instead of 11.5k). Output is unchanged.

• Measured against 0.2.3 on the Criterion suites (benches/compress.rs,
  benches/decompress.rs, pinned to one core, alternating runs): every
  compression and decompression case without a dictionary is within ±2%,
  and 64-byte and 1 KiB inputs execute 0.3% more instructions per call.
  Compression with a dictionary (benches/dictionary.rs, trained 64 KiB
  dictionary, JSON-like records) runs at 0.85-0.91x zstd 1.5.7's time at
  levels 16 and 19 on 100 and 1000 records, 1.09-1.19x at levels 1-9, and
  1.20-1.29x for a single 107-byte record.

• New fuzz target compress_dictionary and decode_dictionary, and the
  dictionary Criterion benchmark; the parallel benchmark gains a
  per-level group.