M11: Optimize keeps a JPEG's colour transform (#1201)

Optimize decoded DCT images with the generic JPEG decoder, which converts
three components from YCbCr to RGB whenever the JPEG itself doesn't say
otherwise, and then dropped /DecodeParms. An RGB JPEG stored untransformed
(/ColorTransform 0 and no Adobe marker) therefore came out in other colours
when recompressed, resampled or merged from strips.

The samples are now read with the colour transform ISO 32000-2 §7.4.8
gives them: an Adobe APP14 marker's flag, else /ColorTransform (default 1).
Untransformed samples are taken as stored, and the result is written as a
plain YCbCr JPEG (or Flate), which needs no /DecodeParms. When the marker
and /ColorTransform disagree, a value is out of range, the parameters are
not paired with the filter as §7.4 pairs them, or the decoder reads the
components otherwise (named R, G and B), the image is left as it is.

The tests draw each image with PdfCraft's renderer before and after
Optimize: RGB JPEGs with and without an Adobe marker under each
/ColorTransform, CMYK JPEGs (still left alone) and JPEG strips merged into
one picture.

Part of #1201.

parity/acrobat-features.toml

@@ -7284,8 +7284,8 @@ milestone = "M11"
 status = "partial"
 commands = ["optimize.advanced"]
 tools = ["doc_optimize"]
-evidence = ["crates/optimize/tests/optimize.rs::images_are_measured_where_drawn_and_downsampled", "crates/optimize/tests/optimize.rs::settings_choose_what_happens"]
-notes = "JPEG (quality steps) and ZIP; no JPEG 2000"
+evidence = ["crates/optimize/tests/optimize.rs::images_are_measured_where_drawn_and_downsampled", "crates/optimize/tests/optimize.rs::settings_choose_what_happens", "crates/optimize/tests/jpeg_color_transform.rs::optimize_keeps_the_colours_of_an_rgb_jpeg_whatever_its_colour_transform"]
+notes = "JPEG (quality steps) and ZIP; a JPEG is decoded with its colour transform (Adobe marker, else /ColorTransform), and one whose marker and /ColorTransform disagree is left as it is; no JPEG 2000"
 
 [[feature]]
 id = "optimize.mono-compression"