[Lightbox] Always rely on Expo Image cache

[gaearon]

Removes our own caching layer for image dimensions. Instead, rely on onLoad callback from expo-image which tells us the dimensions. So if the image is cached by expo-image, these will come through via onLoad.

In the lightbox, until onLoad fires for the full image, we'll use either the embed record dimensions (if available), or fall back to the already fetched thumbnail dimensions (determined by onLoad in the feed).

What this gives us:

• No more duplicate requests (via RN Image vs Expo Image) for missing dimension embed records
• The lightbox is properly animated if onLoad in feed ran in time — since we know the aspect ratio early in that case

Test Plan

Verify that images animate when opening. Notably, images on posts like https://bsky.app/profile/docdre.bsky.social/post/3l6lzzqhxwh2o (which has no image dimensions in embed record) will also animate now.

Comment out the onLoad calls in AutoSizedImage.tsx and Gallery.tsx. Verify they aren't essential — the lightbox works without them. For posts with no dimensions in the embed (https://bsky.app/profile/docdre.bsky.social/post/3l6lzzqhxwh2o), the lightbox would not animate without those onLoad calls — similar as before this PR. It should still display though. Posts with dimensions in embed records should continue animating even without those onLoad calls.

Verify images appear cropped in feed similarly as before. Verify the animation from the cropped ones works.

Not sure how to verify this, but I'd expect that we no longer fire duplicate requests for images with missing dimensions.

[github-actions]

Old size	New size	Diff
8.01 MB	8.01 MB	4 B (0.00%)

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[haileyok]

makes sense, and works as described on the test image linked.