fix android thumbnail cache invalidation

[zerox80]

summary

this fixes stale thumbnails on android when an image gets replaced but the old cached bitmap is still around.

the thumbnail url now uses a proper cache token order:

explicit etag, then remote etag, then etag, then blank

also updated the android save paths that learn a fresh server etag after download or upload, so they persist it into both etag and remoteEtag.

details

• keep the existing coil cache setup
• make remoteEtag the main thumbnail cache token when available
• save download etags into both local etag fields
• resolve upload etags with one metadata read if the upload result is blank
• update existing db rows for content uri uploads instead of inserting folder-list rows
• preserve a usable remoteEtag when copying files

testing

• ./gradlew :opencloudApp:testOriginalDebugUnitTest --tests "eu.opencloud.android.presentation.thumbnails.ThumbnailsRequesterTest"
• ./gradlew :opencloudData:compileDebugAndroidTestKotlin
• git diff --check

[guruz]

btw, this PR needs a rebase :)

explicit etag, then remote etag, then etag, then blank

I see this also does some sha256 computation and stores the value? This should not be done, especially not into etag DB field... let's keep ETag for things really by ETag

Maybe it could be two commits, one for the ETag write changes, one for the thumbnail changes?