This pull request primarily updates the documentation in README.md to provide a clearer, more comprehensive, and structured explanation of LightProto's features, usage, and differences from protobuf-net. It also adds a new test project to the solution. The most significant changes include a major rewrite and expansion of the serialization API documentation, clarification of .NET Standard and Unity support, and improved guidance on surrogates and runtime type handling.

Documentation improvements and API clarification:

• Thoroughly rewrote and reorganized the serialization API section to clearly explain generic, dynamic, non-generic, and .NET Standard–specific APIs, including detailed code samples and guidance on ProtoReader/Writer resolution order.
• Clarified differences from protobuf-net, especially regarding partial classes, surrogates, runtime type model, and string interning, and introduced new sections for StringIntern and RuntimeTypeModel usage.
• Improved instructions and explanations for working with .NET Standard, including explicit notes about static virtual interface members and Unity/IL2CPP compatibility.
• Enhanced the migration guide and usage notes for surrogates, including clearer attribute precedence and updated code examples. [1] [2]

General documentation and language improvements:

• Improved the overall clarity, grammar, and formatting throughout the README, including the features list, code samples, and section headings. [1] [2] [3]

Project structure:

• Added the new test project LightProto.Cs9Tests to the solution file LightProto.slnx.