Pre-caches TypeMetadataWrapper instances for complex properties,
eliminating repeated GetWrapper dictionary lookups in serialization
and deserialization. Adds ComplexPropertyIndex and ComplexPropertyCount
fields, and PropertyTypeWrappers array to TypeMetadataWrapper. Refactors
scan, write, and populate passes to use cached wrappers, improving
performance for deep and polymorphic object graphs. Updates benchmarks
to focus on FastMode variants. No breaking changes; internal efficiency
improved.