chore: upgrade project to .NET 9

Author: engineering87

src/STMSharp.Benchmarking/STMSharp.Benchmarking.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>

src/STMSharp.Tests/STMSharp.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -16,7 +16,7 @@
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.1">
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>

src/STMSharp/Core/STMVariable.cs

@@ -12,6 +12,10 @@ public class STMVariable<T> : ISTMVariable<T>
         private T _value;
         private int _version;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="STMVariable{T}"/> class with the specified initial value.
+        /// </summary>
+        /// <param name="initialValue"></param>
         public STMVariable(T initialValue)
         {
             _value = initialValue;

src/STMSharp/STMSharp.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net9.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <Title>STMSharp</Title>