LR-PROF-CAMERACOLOR: read and keep DNG ProfileGainTableMap (not rendered)

Parse ProfileGainTableMap (DNG 1.6) and ProfileGainTableMap2 (DNG 1.7):
both versions, DNG 1.7 precedence (version 2 in IFD 0, then the raw IFD;
version 1 in the raw IFD, then IFD 0), u8/u16/f16/f32 gains, gamma.
Malformed tags (wrong size, zero or huge grids, non-finite or negative
gains, bad spacing or gamma) are ignored, never allocated for.

Byte order: the specification gives this tag no byte order of its own,
unlike opcode lists, so the payload is read in the file's byte order with
a big-endian fallback; a wrong-order read can't pass the size checks.
The module docs quote the DNG 1.6 "Byte Order" rule.

The map is kept in ColorData, written back by the DNG writer (version 1,
or version 2 when its gamma isn't 1) and dropped from merge outputs, whose
geometry no longer matches the capture's active area. It is not applied
to the render: Lightroom Classic renders Apple ProRAW without it.
Supersedes the parser of #273.

The CC0 iPhone 12 Pro ProRAW from raw.pixls.us joins the corpus.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

xtask/src/main.rs

@@ -341,6 +341,9 @@ const RAW_SAMPLES: &[(&str, &str)] = &[
         "dng-adobe-canon-5d3-lossy.dng",
         "https://raw.pixls.us/getfile.php/1023/nice/Adobe%20DNG%20Converter%20-%20Canon%20EOS%205D%20Mark%20III%20-%20Lossy%20JPEG%20compression%20%283:2%29.DNG",
     ),
+    // Apple ProRAW (iPhone 12 Pro, iOS 14.3): LinearRaw LJ92 tiles, ProfileToneCurve, ProfileGainTableMap, a sky matte.
+    // sha256 e91e77a4533ed7cce551d83330676ea5c47dd5e55fb38adda7819366afdbdfc2
+    ("dng-apple-iphone12pro-proraw.dng", "https://raw.pixls.us/data/Apple/iPhone%2012%20Pro/IMG_1361.DNG"),
     (
         "dng-canon-5d3-14bit-small.dng",
         "https://raw.pixls.us/getfile.php/2204/nice/Canon%20-%20EOS%205D%20Mark%20III%20-%2014bit%2014bit%20%282.3471882640587%29.dng",