Split sorter code

[slimbuck]

This PR organises a few engine files without changing functionality:

• move gsplat sorter worker into its own file
• clean up app-base graphics device calls

[Copilot]

Pull Request Overview

This PR extracts the inline SortWorker into its own file and tidies up how the graphics device is updated in the app loop without changing existing functionality.

• Extract SortWorker into gsplat-sort-worker.js and update instantiation in GSplatSorter
• Add GraphicsDevice.update() as a wrapper for updateClientRect()
• Refactor AppBase to use the new update() and inline frameStart/frameEnd calls within render()

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/scene/gsplat/gsplat-sorter.js	Import SortWorker, pull out message handler, simplify worker setup
src/scene/gsplat/gsplat-sort-worker.js	New file containing the extracted SortWorker function
src/platform/graphics/graphics-device.js	Add update() method that calls updateClientRect()
src/framework/app-base.js	Replace direct updateClientRect() with graphicsDevice.update(), move frameStart/frameEnd into render()

Comments suppressed due to low confidence (3)

src/platform/graphics/graphics-device.js:902

• [nitpick] Add a JSDoc comment to update() explaining that it wraps updateClientRect() to improve maintainability.

    update() {

src/platform/graphics/graphics-device.js:902

• Consider adding unit tests for GraphicsDevice.update() to ensure updateClientRect() is correctly invoked.

    update() {

src/scene/gsplat/gsplat-sort-worker.js:1

• [nitpick] Add a module-level comment or JSDoc to gsplat-sort-worker.js describing the purpose of SortWorker for better clarity.

// sort blind set of data