This pull request modernizes the OPC UA .NET codebase and tests, removes .NET Standard 2.0 support from certificate/security code, and updates test code to use C# 12 and .NET 8+ features for clarity and maintainability.
- Certificate and BouncyCastle interop files (e.g., CertificateBuilder.cs, X509Extensions.cs, X509SignatureFactory.cs) are refactored to drop NETSTANDARD2_0 support and use modern .NET APIs and conditional compilation.
- Test code across the codebase is updated to use default, strongly-typed Parse methods, collection expressions, and improved async/await patterns.
- Exception handling and assertions in tests are modernized, and test method naming is made consistent with Async suffixes.
- The project and build files are updated to clarify Roslynator analyzer usage and remove obsolete netstandard tags.
- General code and test cleanup includes improved null safety, type safety, and removal of deprecated or unused code.
- let all Xml encoders and decoders follow the dispose pattern, similar to all the other encoders.
- Add fuzz targets for Xml and binary indempotent fuzzer.
- add a ReadOnlySpan<byte> signature for WriteByteString
- add ArrayPool based IBufferWriter<byte> to support encoding of large byte string with buffers
- add Azure DevOps ci pipeline tests with known artifacts that caused fuzzing errors, to catch regressions.
Marc Schier