Fix lazy-loaded image source extraction

[calmplay]

Summary

• promote common lazy image source attributes when an image src is a data:image placeholder
• include data-original, data-lazy-src, data-actualsrc, and data-backup in lazy-image cleanup
• keep small placeholder images when they have an alternate lazy source so standardization can resolve them

Moved this fix here after maintainer feedback on obsidianmd/obsidian-clipper#896 that the change belongs in Defuddle.

Tests

• git diff --check
• npm test
• npm run build
• npm run lint:innerhtml
• npm run size