Feature: Add Canon CR3 raw file support and shared ISOBMFF box walker

[purno998]

Summary

• Introduces a shared ISO Base Media File Format (ISOBMFF) box-walker that handles standard/large-size boxes, EOF-terminated boxes, and uuid boxes with automatic usertype parsing. Designed so existing MP4/QuickTime/HEIF readers can migrate onto it in later, CR3 is the first consumer.

• Adds Cr3MetadataReader and a three-tier handler hierarchy (Cr3Handler → Cr3CanonUuidHandler / Cr3PreviewUuidHandler) that decodes all three Canon UUID blocks found in CR3 files:

  • CMT1–CMT4 — TIFF blobs fed into the existing ExifTiffHandler, populating ExifIFD0Directory, ExifSubIFDDirectory, CanonMakernoteDirectory, and GpsDirectory without any new TIFF parsing logic.
  • XMP UUID — raw XMP packet delegated to XmpReader.
  • Preview UUID — PRVW box header decoded for preview dimensions.
  • THMB / CNCV — thumbnail dimensions and compressor version string stored in the new Cr3Directory.
  • Routes FileType.Crx through ImageMetadataReader.

• Extends CanonMakernoteDirectory and CanonMakernoteDescriptor with tags present on EOS R / RF-mount bodies: FocalType, FocusBracketing, Clarity, HDR-PQ, five additional 0x40xx array tags, and 30 RF lens entries. Fixes FlashDetails to use a proper bitmask. Updates Contrast, Saturation, and Sharpness descriptors to handle signed
  int16 adjustment values from newer bodies while preserving existing Low/Normal/High labels for older cameras.

Notable design decisions

• No new TIFF parsing. CMT1–CMT4 are self-contained TIFF byte streams; reusing TiffReader + ExifTiffHandler. FixedRootExifTiffHandler overrides setTiffMarker to push the correct root directory class (ExifSubIFD, Canon makernote, GPS) before IFD traversal begins.

• Existing readers untouched. Mp4Reader, QuickTimeReader, and HeifReader are not modified. The shared walker is user by CR3 first, migrating the three legacy readers is a deliberate follow-up to keep this PR reviewable.

• Backward-compatible descriptor changes. The specific values that old Canon cameras write for Contrast/Saturation/Sharpness (0, 1, 0xFFFF) continue to return "Normal", "High", "Low". Only values outside that set use the new signed-integer path.

Sample output — Canon EOS R8

[CR3]
  Major Brand                 = crx
  Minor Version              = 1
  Compatible Brands     = crx , isom
  Compressor Version   = CanonCR3_001/00.11.00/00.00.00
  Thumbnail Width        = 160
  Thumbnail Height       = 120
  Preview Width             = 1620
  Preview Height            = 1080

[Exif IFD0]
  Make                           = Canon
  Model                         = Canon EOS R8
  Image Width              = 6000 pixels
  Image Height             = 4000 pixels
  Orientation                = Top, left side (Horizontal / normal)
  Date/Time                  = 2023:08:24 21:40:55
  X Resolution               = 350 dots per inch
  Y Resolution               = 350 dots per inch

[Exif SubIFD]
  Exposure Time           = 1/250 sec
  F-Number                   = f/10.0
  ISO Speed Ratings     = 25600
  Date/Time Original     = 2023:08:24 21:40:55
  Focal Length               = 240 mm
  Lens Model                 = RF24-240mm F4-6.3 IS USM
  Lens Serial Number    = 2682002230
  Body Serial Number    = 023021003574

[Canon Makernote]
  Record Mode              = CR3+JPEG
  Quality                         = RAW
  Focal Type                  = Zoom
  Lens Type                   = Canon RF 24-240mm F4-6.3 IS USM
  Short Focal Length    = 24 1
  Long Focal Length     = 240 1
  Max Aperture             = f/6.3
  Exposure Mode          = Auto exposure
  Metering Mode           = Evaluative
  Flash Mode                 = No flash fired
  Flash Details              = E-TTL
  Contrast                     = Normal
  Saturation                   = Normal
  Focus Bracketing       = Disable
  Clarity                          = 0
  HDR PQ                       = Off
  Firmware Version        = Firmware Version 1.0.0
  Image Type                 = Canon EOS R8

[GPS]
  GPS Version ID           = 2.300

[XMP]
  xmp:Rating                  = 0

[File Type]
  Detected File Type Name    = CRX