+ add ShrinkIt NuLZW building block

[Hawkynt]

What changed

Adds the Apple II NuFX/ShrinkIt RLE + LZW primitive to Compression.Core.Dictionary.Lzw.

NuLzwCodec implements both native ShrinkIt dialects:

• LZW/1 — ProDOS ShrinkIt behavior, dictionary reset every 4096-byte chunk, embedded CRC-16/XMODEM over zero-padded expanded chunks
• LZW/2 — GS/ShrinkIt behavior, dictionary persistence across useful LZW chunks, reset when compression falls back, thread-level integrity supplied by NuFX
• 4096-byte chunking with final zero-fill and caller-supplied logical expanded length on decode
• ShrinkIt delimiter RLE (0xDB by default), including delimiter escaping and 256-byte runs
• 9→12-bit LSB-first codes with ShrinkIt's early-change width transition
• 0x100 clear code and the rare dictionary-full-at-block-boundary deferred-clear case
• raw/RLE/LZW per-chunk fallback decisions matching ShrinkIt economics
• tolerance of the historical trailing pad byte
• tolerance of the unreliable LZW/2 compressed-size recovery word emitted incorrectly by some Macintosh tools; actual bit consumption + requested expanded length remain authoritative, so true truncation is still rejected

A benchmarkable NuLzwBuildingBlock uses LZW/2 and prefixes only the expanded length required by the generic raw-building-block contract; NuLzwCodec itself emits/consumes the native bytes used inside NuFX.

Tests

Coverage includes CRC-16/XMODEM, canonical empty headers, partial/exact/multi-4K chunks, delimiter/run-heavy data, deterministic incompressible data, long persistent LZW/2 dictionaries across code-width changes, LZW/1 CRC corruption, trailing-pad tolerance, malformed Macintosh size hints, building-block roundtrip, and actual bitstream truncation rejection.

Behavior was cross-checked against Apple II File Type Note $e0/8002, NuFX final-revision documentation, and current CiderPress II compatibility behavior. The NuFX .shk/.sdk container remains separate in #128.