Use AssetListLoader to load assets in AppBase.preload

[lucaheft]

Description

Uses AssetListLoader in AppBase.preload to load assets marked as preload.

I also changed the fetching of assets to filter by loaded as well. By the time preload is called some assets might already be loaded. (Wasm modules, as well as some assets which are already loading because they were added to the asset registry. See #3107)

Also added tests for preload

Fixes #4185

Checklist

• I have read the contributing guidelines
• My code follows the project's coding standards
• This PR focuses on a single change

[Copilot]

Pull request overview

This PR refactors the AppBase.preload method to use the AssetListLoader utility for loading preload-marked assets, replacing the previous manual asset loading and event handling implementation. It also adds filtering to exclude already-loaded assets before starting the preload process, and includes comprehensive tests for the preload functionality.

Key changes:

• Replaced manual asset loading loop with AssetListLoader for cleaner code
• Added filter to exclude already-loaded assets from the preload process
• Added test coverage for preload functionality with both positive and negative test cases

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/framework/app-base.js	Refactored preload method to use AssetListLoader instead of manual asset loading; added filtering for already-loaded assets
test/framework/application.test.mjs	Added comprehensive tests for preload functionality covering both assets with preload=true and preload=false scenarios

Comments suppressed due to low confidence (1)

src/framework/app-base.js:711

• Avoid automated semicolon insertion (90% of all statements in the enclosing function have an explicit semicolon).

        const assets = this.assets.filter(asset => asset.preload === true && asset.loaded === false)

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[Copilot]

The AssetListLoader only fires 'progress' events on successful asset loads, not on errors. This changes the behavior from the previous implementation where preload:progress was fired for both successful loads and errors. This means if some assets fail to load, the progress will not reach 1.0 (100%). Consider also handling the 'error' event from AssetListLoader, or document this behavior change.

Suggested change

	assetListLoader.on('progress', onAssetLoad);
	assetListLoader.on('progress', onAssetLoad);
	assetListLoader.on('error', onAssetLoad);

[lucaheft]

There exists no error event for AssetListLoader. We would need to make adjustments to the AssetListLoader class to make this work.