feat(dng)!: migrate DNG decode/encode to gamut-dng; delete the binrw TIFF layer

[justin13888]

Closes #21. Also completes the deletion scope of #20 (src/tiff/, tiff-parser, binrw) — #20 can close when this merges.

Stacked on #45 (base 20-migrate-tiff-parser-gamut-ifd); merge order #42 → #44 → #45 → this.

What is Delivered

• Decode on gamut_dng::DngDecoder — uncompressed, Deflate, lossless JPEG, and DNG 1.7 JPEG XL (iPhone ProRAW) all decode through gamut, replacing hand-rolled strip/tile reads, the DNG lossless-JPEG path, and the jxl-oxide DNG tile decoder (codecs/jxl.rs deleted; dng-decode no longer pulls jxl-decode). Metadata tags gamut-dng doesn't type yet (NoiseProfile, ProfileToneCurve) are read from the decoder's verbatim RawTag extras — consumer-side mapping, not a workaround.
• Bridging per the gamut#253 surface (the API that shipped deliberately different from the original ask): RawLevels per-cell f64 blacks → sensor [u16;4] (exact in the uniform/2×2 cases), white()[0] → u16, active_area/default_crop → Rect, CFA codes → CfaPattern, CameraProfile → matrices/illuminants/as-shot-neutral/analog-balance/baseline-exposure. No double linearization — raw sample semantics unchanged, black-level handling stays in transforms/.
• Encode on gamut_dng::DngEncoder (LinearRaw, 3 planes); DngExportConfig → DngEncodeConfig per the issue.
• The binrw TIFF layer is gone: src/tiff/ (parser/types/tags/writer/metadata_helper), the tiff-parser feature, the binrw dep, the public TiffParser/TiffWriter/TiffValue/TiffTag API, and the parser-internal tests. tests/dng_check.rs is ported to the gamut-ifd tree (structural DNG assertions keep feeding gamut#174). In-repo lossless JPEG + bit pump remain only for CR2/NEF/ARW and are re-gated accordingly.

Breaking (0.x, accepted)

tiff module + tiff-parser feature removed; DngExportConfig renamed; DNG 1.7 JXL raw data reports decoded bit depth 16 (full-range, reference-SDK semantics — noted in DngMetadata::bit_depth docs).

Process note

The implementation agent for this PR was cut off mid-work by a session limit; I completed the remaining slices by hand (final DngEncodeConfig rename sites, a closure-lifetime fix, the dng_check port, prelude cleanup, dead-code deletion, ljpeg re-gating) and ran the full verification below from scratch afterward.

Verification Done

• cargo test --workspace — 383 passed, 0 failed
• cargo test -p rawshift-image --features full — 532 passed, 0 failed, fixtures fetched and ran: dng_check (1) on the gamut-ifd tree, raw_decode_fixtures (10) including dng_metadata_extraction/dng_format_detection against the real iPhone ProRAW DNG (7.6 s wall — the 40 MB files really decode), plus the ARW suite from feat(formats)!: migrate ARW/CR2/NEF/CR3 IFD walking to gamut-ifd #45 unchanged
• cargo test -p rawshift-image --features serde — 365 passed
• cargo clippy workspace + --features full, -D warnings — both clean
• Standalone builds --no-default-features --features {dng,arw,cr2,nef} — zero errors and zero warnings each (includes a fix making the LinearRaw match config-neutral in single-format builds)
• Residual greps — no binrw in any manifest or the lockfile, no crate::tiff, no tiff-parser
• cargo fmt --check + lefthook — green