Use newest Npgsql when targeting net8.0 and above (#13724)

We are currently using Npgsql 8.0 because that's the last version that's
still compatible with .NET Standard 2.0/netfx; but it seems wrong to
force an older version of Npgsql on modern .NET users just because netfx
users require it

So for the versions of the PgVector MEVD provider targeting
net8.0/net10.0, use the latest Npgsql 10.0; netstandard2.0/net462 still
use Npgsql 8.0. It's not ideal to use different versions of Npgsql
across different TFM targets of the same library, but it seems like the
lesser of the possible evils here.

This incidentally also takes care of the ReloadTypesAsync problem in
#13706.

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: roji

dotnet/Directory.Packages.props

@@ -89,7 +89,7 @@
     <PackageVersion Include="ModelContextProtocol" Version="0.4.0-preview.3" />
     <PackageVersion Include="MSTest.TestFramework" Version="3.8.0" />
     <PackageVersion Include="Newtonsoft.Json" Version="13.0.4" />
-    <PackageVersion Include="Npgsql" Version="8.0.7" />
+    <PackageVersion Include="Npgsql" Version="10.0.2" />
     <PackageVersion Include="OData2Linq" Version="2.2.0" />
     <PackageVersion Include="OllamaSharp" Version="5.4.12" />
     <PackageVersion Include="OpenAI" Version="2.9.1" />

dotnet/src/VectorData/PgVector/PgVector.csproj

@@ -32,7 +32,9 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
     <PackageReference Include="Microsoft.Extensions.AI.Abstractions" />
-    <PackageReference Include="Npgsql" />
+    <PackageReference Include="Npgsql">
+      <VersionOverride Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net8.0'))">8.0.7</VersionOverride>
+    </PackageReference>
     <PackageReference Include="Pgvector" />
   </ItemGroup>