chore: add hrynco common library solution

- add the standalone HrynCo.Common solution and projects
- include the shared common library source and tests
- add package metadata and a repo gitignore

HrynCo.Common.Tests/HrynCo.Common.Tests.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+        <IsPackable>false</IsPackable>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="FluentAssertions" Version="8.2.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.0"/>
+        <PackageReference Include="xunit" Version="2.9.3"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.0">
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+            <PrivateAssets>all</PrivateAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\HrynCo.Common\HrynCo.Common.csproj"/>
+    </ItemGroup>
+
+</Project>