v0.1.0

Added

• Butteraugli.compare/5 and compare!/5 — compute the butteraugli perceptual
  difference between two packed-binary images, returning a Butteraugli.Result
  with score (max-norm distance), pnorm_3 (libjxl 3-norm aggregation), and
  an optional diffmap.
• Butteraugli.Reference — new/4, new!/4, compare/3, compare!/3 for
  reusing one prepared reference across many candidates (~2× faster per compare
  in a quality-search loop). compare/3 takes prefer: :speed | :memory
  (default :speed); :memory runs a strip-bounded walker with bounded peak
  memory and per-strip cancellation, trading away the speedup.
• Input formats selectable via the :format option: :rgb888 (default, u8
  sRGB) and :linear_rgb (f32 linear RGB).
• Tuning parameters :intensity_target (display brightness in nits, crate
  default 80.0) and :hf_asymmetry (added-vs-removed high-frequency weighting,
  crate default 1.0). On Butteraugli.Reference these are baked in at
  new/4 time.
• Optional difference map via :compute_diffmap (default false). Diffmaps are
  cropped back to the input size; images smaller than 8×8 are padded up to
  butteraugli's 8×8 floor and scored.
• Cooperative cancellation: Butteraugli.CancelRef.new/0 and
  Butteraugli.cancel/1. The metric runs on a dirty scheduler and polls the
  cancel ref at strip boundaries, freeing the CPU promptly. A cancel ref is
  single-use and can cover a whole batch.
• Wall-clock timeouts via the :timeout option, returning {:error, :timeout}.
• Optional Vix integration (Butteraugli.Vix.compare/2, Butteraugli.Vix.reference/2),
  available when :vix is a dependency; images are coerced to 8-bit sRGB.
• Precompiled NIFs via rustler_precompiled for aarch64/x86_64 macOS,
  gnu/musl Linux, and x86_64 Windows, across NIF versions 2.15–2.17, so
  the Rust toolchain is not required on covered targets.

Notes

• butteraugli is pinned to a git revision because the cooperative-cancellation
  API (*_with_stop) has not yet landed in a crates.io release. This will move
  to a versioned dependency once available.
• The underlying crate is a port of Google's butteraugli implementation from
  libjxl.