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.
Refactored client-side logic to support batching of service requests, ensuring compliance with operation limits and improving scalability. Added telemetry and activity tracing using `ActivityTraceFlags` for better observability, including metrics collection and logging. Enhanced error handling with descriptive exception messages and improved certificate validation.
Introduced a comprehensive suite of unit tests for `SessionClientBatchTests.cs` and `ClientBaseTests.cs`, covering batching, error scenarios, and edge cases. Added helper classes for testing logging, metrics, and activity tracing. Updated tests to align with modern C# practices, including nullable reference types and collection initializers.
Improved code consistency, readability, and maintainability by standardizing method signatures, simplifying redundant patterns, and removing legacy constructs. Updated XML documentation and added conditional compilation for .NET 8.0+ compatibility.
Marc Schier