Feature request draft — expose SparkRenderer LoD options in 3d-tiles-rendererjs-3dgs-plugin

Target repo: https://github.com/WilliamLiu-1997/3D-Tiles-RendererJS-3DGS-Plugin

Title: Allow passing lodInflate / lodSplatScale (and other SparkRenderer LoD settings) through sparkRendererOptions

Body:

The plugin's sparkRendererOptions currently forwards a fixed allowlist to the shared SparkRenderer: premultipliedAlpha, encodeLinear, maxStdDev, minPixelRadius, maxPixelRadius, minAlpha, enable2DGS, preBlurAmount, blurAmount, clipXY, focalAdjustment, sortRadial, minSortIntervalMs, depthTest, depthWrite.

It does not include the SparkRenderer LoD controls that SparkJS's own viewer sets, notably:

lodInflate (default true in SparkJS's viewer) — inflate LoD splats so opacity ≤ 1.0; visibly improves blending of coarse/merged LoD splats.
lodSplatScale — scales the active-splat budget / LoD detail.

Why it matters: when rendering 3D Tiles tilesets whose content is baked LoD Gaussian splats (e.g. converted from SparkJS .RAD or PlayCanvas Streamed SOG), the coarse tiles are pre-merged representatives. Without lodInflate, those coarse splats render under-opaque and don't blend the way they do in SparkJS's native viewer, so the same data looks sparser/spikier through the plugin than in sparkjs.dev's explore viewer.

Current workaround: reach the shared renderer via getSparkRendererForScene(scene) and set spark.lodInflate = true; spark.lodSplatScale = …; spark.lodDirty = true; directly. This works but relies on internal properties rather than the public sparkRendererOptions surface.

Request: add lodInflate and lodSplatScale (and ideally the cone-foveation settings coneFov0/coneFov/coneFoveate/behindFoveate) to the sparkRendererOptions allowlist, and to updateSharedSparkRendererOptions, so they can be set declaratively at plugin construction and at runtime.

This repo (3dtiles-converters) applies the getSparkRendererForScene workaround in viewer.html (applySparkLodSettings) until the option is exposed.