fix: prioritize current frame for single-LOD case (typical volume rendering case)

[aganders3]

Summary

When working with remote rendering, I noticed a bug I introduced in #665 that results in the volume layer stalling until the entire prefetch queue drains.

That PR rewrote updateChunksForVolume and replaced the per-chunk isCurrentLOD = chunk.lod === currentLOD_ derivation with a markVolumeChunkVisible(chunk, isFallbackLOD) helper that computes isCurrentLOD = !isFallbackLOD. When currentLOD === fallbackLOD, only the current-LOD pass runs, so every chunk is marked with isFallbackLOD=false, isCurrentLOD=true. computePriority then returns visibleCurrent (priority 2 under createPlaybackPolicy) instead of fallbackVisible (priority 0) — and since prefetchTime is priority 1 in the same policy, the current frame's chunks land in the queue behind the entire prefetch backlog.

This restores previous behavior by getting both isFallbackLOD and isCurrentLOD from the chunk's own chunk.lod inside markVolumeChunkVisible, so for single LOD (we configure this typically by setting min LOD === max LOD in the policy) both flags are true and computePriority returns fallbackVisible as it did before #665.

Tests & Checks

I confirmed this fix restores the expected (previous) behavior in a reef idetik-remote session.

[shlomnissan]

LGTM 👍

[czi-github-helper]

🎉 This PR is included in version 0.22.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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