v4.0.0 preview is released

[SKProCH]

This is a complete rework of internals of the library:

• Replaced inheritance-based image loaders with a composable loading pipeline
• Added pipeline presets and a builder for customizing source resolution, transport, decoding, and caching
• Introduced lease-based image ownership with proper control lifecycle handling
• Kept the existing loaders as compatibility facades over the new pipeline

Migration guide: #48 (comment)

Please, try it and share your feedback in comments.