Fix blurry fullscreen/peek animated and custom emoji

[anriltine]

Summary

• Peek / enlarged sticker & custom emoji decoded Lottie/WebM into a small raster buffer (~200px for custom emoji) and displayed it on Retina, which looks soft/pixelated — same class of bug as tdesktop#31158 / Desktop media-viewer thumb upscale.
• Decode peek animations at native sticker size (capped 512) and slightly enlarge custom-emoji peek layout.
• Add blurThumbnail: (default true) on chatMessageSticker / chatMessageAnimatedSticker; peek/preview pass false so a waiting thumb is sharp-upscaled, not Blur-softened, until the full asset arrives.

Fixes #2296
Related: #2292
Tracking: HyperlinksSpace/HyperlinksSpaceProgram#92

Test plan

• Long-press / peek an animated custom emoji on a 2×/3× device — animation should look crisp, not soft
• Peek a static custom emoji / sticker before and after full download — placeholder should not look Blur-smudged; final frame should be sharp
• Peek a normal animated sticker — still loops correctly at enlarged size
• Inline chat stickers/emoji unchanged (default blurThumbnail: true path)

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