removed some new lang features to support net6.0 and net7.0

Railway/Railway.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
+    <LangVersion>10.0</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <AssemblyName>Just.Railway</AssemblyName>
@@ -13,7 +14,6 @@
     <Copyright>Copyright (c) 2023 JustFixMe</Copyright>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <PackageReadmeFile>README.md</PackageReadmeFile>
-
     <RepositoryUrl>https://github.com/JustFixMe/Just.Railway/</RepositoryUrl>
     
     <EmitCompilerGeneratedFiles Condition="'$(Configuration)'=='Debug'">true</EmitCompilerGeneratedFiles>