UA-.NETStandard

Migrate OPC UA .NET Standard applications from version 1.5.378 to version 2.0.x. Walks consumers through installing the OPCFoundation.NetStandard.Opc.Ua.MigrationAnalyzer NuGet (analyzers UA0001-UA0022, source-generated <Type>Collection shims, runtime compat shim), running `dotnet format analyzers` to apply auto-fixes, and walking the residual manual patterns. Use when asked to "migrate to v20", "update from 1.5.378", "fix v20 build errors", "migrate OPC UA code to 2.0", "update to new Variant API", "fix ArrayOf migration", "update NodeId readonly struct", "migrate from object to Variant", "fix CS0246 on <Type>Collection wrappers", "fix CS0246 on CertificateValidator", or "address UA00xx / MIG01 warnings". Sample triggers: user says "my project targets 1.5.378 and I need to update to v20"; user provides build errors after updating NuGet packages to 2.0; user asks "how do I update my custom NodeManager for v20?"; user says "fix all the CS0029 errors after upgrading to v20".