gigapdf-lib v0.69.0

Image-watermark release: stamp a raster image across any range of pages, with
the same ergonomics as the existing text watermark. The text watermark is
unchanged.

Added

• Image watermark. Stamp a raster image over pages —
  addImageWatermark (SDK) / add_image_watermark (core) /
  gp_add_image_watermark (FFI). Accepts PNG / JPEG / WebP / GIF / AVIF
  source images and supports per-watermark opacity, anchoring
  (center + four corners) with offsets, rotation (about the image center),
  scaling to a target size (aspect-follow), and an optional tiling grid.
  The image XObject is embedded once and referenced on each target page,
  reusing the existing image-embed/raster-transcode pipeline. The text
  watermark and add_image behavior are unchanged.