Upgrade target framework from net6 to net8.0 and fix package compatibility

- Updated TargetFramework from net6 to net8.0 to resolve compatibility issues
- Added Platform.Data.Doublets package reference with compatible version 0.17.2
- This resolves the NU1202 error where Platform.Data.Doublets.Sequences 0.5.2
  requires net7.0 or higher target framework

Addresses issue #42: The original request was to upgrade from netcoreapp3.0
to netcoreapp3.1, but the project has evolved and now needs a modern target
framework to work with current dependencies.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: konard

Comparisons.SQLiteVSDoublets.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
@@ -13,6 +13,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(Configuration)'=='Release'">
+    <PackageReference Include="Platform.Data.Doublets" Version="0.17.2" />
     <PackageReference Include="Platform.Data.Doublets.Sequences" Version="0.5.2" />
   </ItemGroup>
 
@@ -21,6 +22,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(Configuration)'=='Debug' AND !Exists('..\Data.Doublets.Sequences\csharp\Platform.Data.Doublets.Sequences\Platform.Data.Doublets.Sequences.csproj')">
+    <PackageReference Include="Platform.Data.Doublets" Version="0.17.2" />
     <PackageReference Include="Platform.Data.Doublets.Sequences" Version="0.5.2" />
   </ItemGroup>