Add Android Preload List

[jkmassel]

What?

Adds an Android preloading system for the Gutenberg editor that prefetches editor dependencies before display, matching the existing iOS implementation.

Why?

The Gutenberg editor requires several API calls and asset downloads during initialization, which can cause slow launch times. This PR introduces a preloading architecture that:

• Pre-fetches API responses (post types, themes, settings) so the editor doesn't need to make network calls during startup
• Downloads and caches JavaScript/CSS asset bundles for faster subsequent launches
• Provides progress feedback to the user during preparation
• Establishes feature parity with the existing iOS preloading system

How?

New Core Components:

• EditorService - Orchestrates loading all editor dependencies with progress tracking
• EditorPreloadList - Pre-fetched API responses injected into the editor JavaScript
• EditorAssetsLibrary (in stores/) - Downloads and caches asset bundles
• EditorHTTPClient - Authenticated HTTP client for WordPress REST API
• RESTAPIRepository - REST API calls with response caching
• EditorURLCache - URL-level caching with configurable policies

New Model Classes:

• EditorAssetBundle - Represents downloaded editor assets
• EditorCachePolicy - Configurable caching strategies (Always, MaxAge, Ignore)
• EditorSettings, EditorDependencies - Editor configuration models
• GBKitGlobal, LocalEditorAssetManifest, RemoteEditorAssetManifest - Asset manifest parsing

Demo App Updates:

• Added SitePreparationActivity and SitePreparationViewModel showing the preloading flow with progress UI

Other Changes:

• Minor iOS test fixes and EditorSettings improvements for consistency
• This PR removes the existing warmup code – a more recent version of androidx.webkit exposes prerenderUrlAsync which we should adopt for this purpose.

Testing Instructions

1. Build and run the Android demo app
2. Select a site configuration
3. Observe the "Site Preparation" screen showing loading progress
4. Tap "Prepare from scratch" to test full loading without cache
5. Tap "Prepare" to test cached loading
6. Verify the editor loads correctly with preloaded data
7. Run make test-android to verify all new unit tests pass

See the tests in #250 for examples of tests sites you can use.

[adalpari]

⛏️Aren't we using injection in the example project? ViewModels can be simply injected.

[jkmassel]

I don't think we are at the moment – I'd be happy to adopt it, but I think it's outside the scope of this PR :)

[adalpari]

Do we want to track the exception here?

[jkmassel]

In this case probably not, because we'll treat a cache failure as a simple cache miss. I've modified this to use runCatching in c64592b, which should hopefully make the intent more clear!