Support JPEG XL format for image optimization

Summary Add support for JPEG XL (JXL) as an output format for image optimization in Imagify. Customer request A customer has requested JPEG XL support for image optimization. The request indicates a need for Imagify to support this modern image format alongside existing WebP/AVIF optimization workflows. Why this matters • JPEG XL offers smaller file sizes and better quality than JPEG for many images. • It is increasingly relevant for modern web performance optimization. • Customers expect Imagify to support the same next-generation formats that are now common in the ecosystem. Expected behavior Imagify should be able to: • detect JPEG XL as a supported format when relevant, • optimize JPEG XL images where applicable, • expose the format in the plugin’s optimization/next-gen generation flow, • keep the feature aligned with current WebP/AVIF support and compatibility constraints. Notes This feature request is based on the customer reque…