* Start on general API formalization
* More API improvements
- Add Engine#onLightUpdate; remove LightUpdateHolder and backend/ClientChunkCacheMixin
- Add Effect#level
- Add VisualizationHelper#queueAdd and #queueRemove for Effects
- Fix PartialModel not assigning bakedModel field when populating on init
- Fix PartialModel.ALL using weak keys instead of weak values
- Make Simple*Visualizer and corresponding inner Builder classes final
- Restore FlatLit#light overload that accepts block and sky light values separately
- Add AbstractBlockEntityVisual#relight overloads that accept Iterator and Iterable
- Reorganize classes in impl.vizualization
* TaskExecutor simplification
- Move TaskExecutor#sync* methods to TaskExecutorImpl
- Move Flag and RaisePlan to impl
- Remove TaskExecutor#scheduleForMainThread and #isMainThread methods
- Remove SyncedPlan
- Add Engine#setupRender
- Remove TaskExecutor parameters from Engine#render* methods
- Convert Engine$CrumblingBlock into an interface
- Unmark RenderContext as NonExtendable to allow fulfilling the purpose described in the doc of VisualizationManager#renderDispatcher
* Remove registry freeze callbacks
- Lazily initialize MaterialShaderIndices
- Rename MaterialShaders#*Shader to #*Source
- Move BackendImplemented to api.backend package
- Pass partial tick to visualizers and Effect#visualize
- Pass partial tick to LitVisual#updateLight
- Remove Visual#init
- Rename LitVisual#initLightSectionNotifier to setLightSectionNotifier
- Add static utility methods to FlatLit
- Remove relight methods from AbstractVisual and add specialized relight methods to AbstractBlockEntityVisual and AbstractEntityVisual to match how vanilla retrieves lightmaps
- Rename AtomicBitset to AtomicBitSet
- Move registry freezing to right before start of initial resource reload
- Also warn if Fabric config JSON is not an object
- Move Flywheel.java to API
- Remove Flywheel.LOGGER and others; add impl-specific and backend-specific loggers
- Remove unused mixins
- Organize imports
