Add JPEG XL format, detector and libjxl-backed codec

[Ram-Pavith]

Adds JPEG XL format support: JxlFormat, header detector (codestream FF 0A and container signatures), metadata, configuration module, and cjxl/djxl-backed encoder/decoder (ImageSharp has no managed JXL codec yet; only cjxl can also transcode legacy JPEG bit-exactly).

Registered in the default Configuration. New detector tests pass (3/3, dotnet test -f net10.0); library builds clean with .NET 10.

Note: PR #3153 is also working on JXL support; this smaller detector + libjxl-delegating codec is offered as an alternative/complement for discussion.

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[JimBobSquarePants]

I’m closing this PR. This approach is fundamentally incompatible with ImageSharp, and I am frustrated that it was submitted without respecting the project’s architecture or contribution process.

ImageSharp is a fully managed library. Launching native executables found on PATH, writing temporary files, and converting through PNG is not an acceptable implementation of JPEG XL support in this library. It defeats a core reason the library exists.

You removed the PR template rather than completing it. You also explicitly acknowledged #3153, which has been open since July. That contributor is undertaking the substantial work needed to implement JPEG XL within ImageSharp’s architecture. Offering an external command-line wrapper as a smaller alternative dismisses the requirements that make that work substantial.

This submission shows a lack of respect for the existing contributor’s work and for the maintainers’ time. Please read and follow the contribution requirements, understand the library’s design, and discuss proposals with the maintainers before submitting further work of this kind.

I will not accept this approach or review revisions intended to make it mergeable.