DropIn Viewer lag fix and Cursor raycast fix

[JawHawk]

First of all, Thanks for all your work.
These are some simple fixes for two performance issues I faced:

1. I was using the DropIn Viewer with R3F but it felt much laggy as compared to general Viewer. I tried to debug and found that the init function was called on every update loop for dropInViewer which was unnecessary and heavy. So isUpdatedForDropInMode check is added to ensure init() runs only once in DropIn mode.

2. I was using the provided default cursor but it moved very abruptly for certain models. This is because requestAnimationFrame would exceed timelimit because intersectSplatMesh would run for more than 250 ms every time. I could narrow it down that it only happened for 3dgs files which had distant blurred spherical splat background.
   Couldn't find the exact reason but for such background consisting models, the data.indexes array length in splat Tree went upto 50000 to 100000. I am still unsure about the function of data indexes in splat tree and what is its functionality. But this issue was resolved by increasing the maximumDepth of splat tree.
   I think increasing this value as the new default is a safe and effective solution, right ?

issue-2025-05-29_20.47.08.mp4

issue-2025-05-29_20.49.40.mp4