Implement Sony ARW6 decoder

[abbradar]

This is an LLM-assisted (Claude Fable) port of my ARW6 reference decoder to rawspeed. The reference decoder's initial implementation was LLM-assisted too, but I've completely reviewed it and rewrote most parts by hand.

The comments were preserved as is from the reference decoder, but I restructured the code to live in a single .cpp, as other decoders here do.

One questionable thing is a custom Plane class which is an owning Array2DRef; I didn't find anything similar in the existing code, but I may be wrong. I've also introduced OpenMP parallelism for tiles and channels. It's clunky because of the exception passing; I didn't use OpenMP before, but AFAIU that's a well-known wart; I'd also love to be corrected.

Fixes #968

[github-actions]

The proposed diff is not clang-formatted.
To make this check pass, download the following patch
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(NOTE: save it into the repo checkout dir for the snippet to work)
https://github.com/darktable-org/rawspeed/actions/runs/32566379854/artifacts/9474187307
... and run:

cd <path/to/repo/checkout> # NOTE: use your own path here
unzip clang-format.patch.zip
git stash # Temporairly stash away any preexisting diff
git apply clang-format.patch # Apply the diff
git add -u # Stage changed files
git commit -m "Applying clang-format" # Commit the patch
git push
git stash pop # Unstast preexisting diff
rm clang-format.patch.zip clang-format.patch

[github-actions]

The proposed diff is not clang-formatted.
To make this check pass, download the following patch
(via browser, you must be logged-in in order for this URL to work),
(NOTE: save it into the repo checkout dir for the snippet to work)
https://github.com/darktable-org/rawspeed/actions/runs/32567908722/artifacts/9474570607
... and run:

cd <path/to/repo/checkout> # NOTE: use your own path here
unzip clang-format.patch.zip
git stash # Temporairly stash away any preexisting diff
git apply clang-format.patch # Apply the diff
git add -u # Stage changed files
git commit -m "Applying clang-format" # Commit the patch
git push
git stash pop # Unstast preexisting diff
rm clang-format.patch.zip clang-format.patch

[abbradar]

Formatted and also cleaned up a bit; decided against an arrow proxy clunkiness after all, and removed the identity LUT.

[github-actions]

The proposed diff is not clang-formatted.
To make this check pass, download the following patch
(via browser, you must be logged-in in order for this URL to work),
(NOTE: save it into the repo checkout dir for the snippet to work)
https://github.com/darktable-org/rawspeed/actions/runs/32568125313/artifacts/9474621151
... and run:

cd <path/to/repo/checkout> # NOTE: use your own path here
unzip clang-format.patch.zip
git stash # Temporairly stash away any preexisting diff
git apply clang-format.patch # Apply the diff
git add -u # Stage changed files
git commit -m "Applying clang-format" # Commit the patch
git push
git stash pop # Unstast preexisting diff
rm clang-format.patch.zip clang-format.patch

[kmilos]

x-ref #972

[abbradar]

Ouch, failed to find it while searching before, thanks