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.
Major overhaul of serialization/deserialization infrastructure:
- Introduced unified Chain API for binary/JSON, enabling multi-deserialization/population with strong IId reference identity (critical for Blazor/DXGrid).
- Added base classes for property accessors/setters and centralized type metadata.
- Implemented ChainReferenceTracker and shared IIdCollectionMergeHelper for reference tracking and collection merging.
- Refactored property access logic to use typed delegates for primitives/enums.
- Updated extension methods and replaced legacy chain/populate interfaces.
- Improved error handling and diagnostics.
- Added comprehensive tests for chain API and reference preservation.
- Minor fixes and performance optimizations throughout.
Loretta