Fix all warnings

[Konard]

gitpod /workspace/Protocols.Lino/csharp (main) $ dotnet test -c Release -f net8
  Determining projects to restore...
  All projects are up-to-date for restore.
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/obj/Release/net8/Parser.peg.g.cs(40,37): warning CS1584: XML comment has syntactically incorrect cref attribute 'IList{Link{string}}' [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/obj/Release/net8/Parser.peg.g.cs(40,43): warning CS1658: Type parameter declaration must be an identifier not a type. See also error CS0081. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/obj/Release/net8/Parser.peg.g.cs(40,48): warning CS1658: Type parameter declaration must be an identifier not a type. See also error CS0081. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/id.cs(7,19): warning CS8981: The type name 'id' only contains lower-cased ascii characters. Such names may become reserved for the language. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/LinksGroup.cs(69,30): warning CS8765: Nullability of type of parameter 'obj' doesn't match overridden member (possibly because of nullability attributes). [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(128,30): warning CS8765: Nullability of type of parameter 'obj' doesn't match overridden member (possibly because of nullability attributes). [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/LinksGroup.cs(37,65): warning CS8625: Cannot convert null literal to non-nullable reference type. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(33,91): warning CS8602: Dereference of a possibly null reference. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(33,91): warning CS8604: Possible null reference argument for parameter 'reference' in 'string Link<TLinkAddress>.EscapeReference(string reference)'. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(36,109): warning CS8604: Possible null reference argument for parameter 'reference' in 'string Link<TLinkAddress>.EscapeReference(string reference)'. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(71,47): warning CS8604: Possible null reference argument for parameter 'id' in 'Link<TLinkAddress>.Link(TLinkAddress id, IList<Link<TLinkAddress>> values)'. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Link.cs(107,104): warning CS8604: Possible null reference argument for parameter 'reference' in 'string Link<TLinkAddress>.EscapeReference(string reference)'. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/Platform.Protocols.Lino.csproj::TargetFramework=net8]
  Platform.Protocols.Lino -> /workspace/Protocols.Lino/csharp/Platform.Protocols.Lino/bin/Release/net8/Platform.Protocols.Lino.dll
/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino.Tests/TupleTests.cs(4,7): warning CS8981: The type name 'id' only contains lower-cased ascii characters. Such names may become reserved for the language. [/workspace/Protocols.Lino/csharp/Platform.Protocols.Lino.Tests/Platform.Protocols.Lino.Tests.csproj::TargetFramework=net8]
  Platform.Protocols.Lino.Tests -> /workspace/Protocols.Lino/csharp/Platform.Protocols.Lino.Tests/bin/Release/net8/Platform.Protocols.Lino.Tests.dll
Test run for /workspace/Protocols.Lino/csharp/Platform.Protocols.Lino.Tests/bin/Release/net8/Platform.Protocols.Lino.Tests.dll (.NETCoreApp,Version=v8.0)
Microsoft (R) Test Execution Command Line Tool Version 17.8.0 (x64)
Copyright (c) Microsoft Corporation.  All rights reserved.

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.

Passed!  - Failed:     0, Passed:    12, Skipped:     0, Total:    12, Duration: 80 ms - Platform.Protocols.Lino.Tests.dll (net8.0)