4.40.0: Adaptive minimal-fetch and HEIC/AVIF iloc fixes

Added

• New includeOffsets option (with expanded: true) returns a metadataRange
  object, {start, end, complete, blocks: [{type, start, end}, ...]}, describing
  exactly where metadata sits in the file, so you can persist just the
  metadata-bearing prefix instead of the whole image. Supports JPEG, PNG, WebP,
  HEIC, AVIF, JPEG XL (container), GIF, and standalone XMP/XML. (#121)
• New length: 'auto' option adaptively fetches only the bytes that contain
  metadata via HTTP Range requests (or filesystem reads / File.slice locally),
  reporting the minimal slice as metadataRange.buffer, bytes read as
  metadataRange.fetched, and IO-call count as metadataRange.requests.
  Requires expanded: true and includeOffsets: true.

Fixed

• HEIC/AVIF: correctly read Exif and XMP from iloc items using
  constructionMethod 1 (idat); these were previously read from the wrong file
  offset, producing garbage tags or none. constructionMethod 2 items are now
  skipped cleanly instead of returning garbage.
• HEIC/AVIF: multi-extent Exif and XMP items are now parsed end-to-end;
  previously only the first extent was read, dropping any tags that spilled into
  a second extent.