support additional class loaders for savables

[riccardobl]

Reimplement deprecated apis needed to fix jMonkeyEngine/sdk#659

[gemini-code-assist]

Code Review

This pull request introduces support for loading Savable classes using additional class loaders provided by the AssetManager during binary import. This is achieved by overloading SavableClassUtil.fromName to accept a collection of class loaders and attempting to load classes through them if the default lookup fails. Feedback focuses on thread safety and performance optimizations: specifically, synchronizing the iteration over additionalClassLoaders to prevent ConcurrentModificationException and caching the class loaders in BinaryImporter to avoid redundant list allocations and GC pressure during object loading.

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