Refactor tests to use _All_True model types throughout
Replaced all usages of legacy test model types (e.g., TestOrder, TestOrderItem, SharedTag, etc.) with new, feature-complete _All_True variants across SignalR test infrastructure, data sources, and service handlers. Updated all generic constraints, method signatures, and test data to use the new types. Added SharedTestBaseModels.cs and SharedTestOrderModels.cs to define abstract bases and concrete _All_True models with full serialization attributes. This enables more thorough and realistic serialization/deserialization testing and future extensibility.
Replaces boolean UseStringInterning with StringInterningMode enum for more granular control (None, Attribute, All). Introduces AcStringInternAttribute for per-property interning configuration. Updates all usages and documentation to reflect the new approach, ensuring explicit and flexible string interning behavior in serialization. Default mode is now All to preserve legacy behavior.
Major overhaul of binary serializer/deserializer tests: split and expand test coverage for primitives, objects, navigation, generics, circular refs, and edge cases. Fix critical bugs in property skipping, string interning, type mismatch diagnostics, nullable assignment, and VarInt decoding. Add WASM-optimized deserialization options with string caching. Switch SignalR compression from Brotli to Gzip and introduce GzipHelper. Add comprehensive StockTaking test models and real-world bug reproductions. Improve diagnostics, test discovery, and add benchmark/utility scripts.
Loretta