Skip auto-applied denoise presets on AI denoised output

[andriiryzhkov]

Fixes #21391

If you have denoise (profiled) as an auto-apply preset, it fires again on the DNG that AI raw denoise produces. The output keeps the source ISO, so an ISO-ranged preset matches it exactly as it matched the original raw – darktable has no way of knowing the work has already been done.

So the DNG now says so itself. The writer stamps Xmp.darktable.neural_restore = "raw-denoise" into the file, dt_exif_read picks it up at import and sets a new DT_IMAGE_AI_DENOISED flag, and _dev_auto_apply_presets leaves denoiseprofile and rawdenoise out of its query for those images – the same trick already used for basecurve in a display-referred workflow. Keeping the marker in the file rather than the database means it survives a manual import, a film roll rescan or a rebuilt library.

Only automatic application is suppressed; you can still enable the module yourself, which is what the thread asked for. A preference switches the stamping off for anyone who doesn't want darktable writing that into their files, and says plainly that this also removes the protection.

Astrophoto denoise deliberately stays out of the skip list – auto-applying it is usually a choice. IPTC DigitalSourceType would be the standards-correct way to announce this to other software, but it's single-valued and sharpening elsewhere sets the same code, so it can't drive the decision and belongs in its own change.

[wpferguson]

Maybe we should think about another way to solve this. Not writing to image files is one of the founding principles of darktable.

Maybe we need to make module auto apply a little smarter.

[andriiryzhkov]

We can think of other way, but lets first align on what actually gets written where:

• The original raw is never modified. We only read it.
• The new DNG is created by darktable. libtiff writes the image data and DNG tags, and then the existing code reopens that file to merge the source EXIF into it. That already happens on master, before this PR.
• This PR adds one XMP property to that same new DNG: Xmp.darktable.neural_restore = "raw-denoise".

[andriiryzhkov]

@wpferguson : does this mean you think this approach is reasonable?

[wpferguson]

So we're just adding a little bit more to what we are already writing. Consider my comment withdrawn 😄

Though auto apply could be a little smarter (not just for this).

[TurboGit]

Thanks!