Bump ReactiveUI.Fody and System.Reactive

Bumps [ReactiveUI.Fody](https://github.com/reactiveui/reactiveui) and [System.Reactive](https://github.com/dotnet/reactive). These dependencies needed to be updated together.

Updates `ReactiveUI.Fody` from 13.2.18 to 19.5.41
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@13.2.18...19.5.41)

Updates `System.Reactive` from 5.0.0 to 6.0.0
- [Release notes](https://github.com/dotnet/reactive/releases)
- [Commits](https://github.com/dotnet/reactive/commits)

---
updated-dependencies:
- dependency-name: ReactiveUI.Fody
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: System.Reactive
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Shadowsocks.WPF/Shadowsocks.WPF.csproj

@@ -53,7 +53,7 @@
     <PackageReference Include="MdXaml" Version="1.21.0" />
     <PackageReference Include="OxyPlot.Wpf" Version="2.2.0" />
     <PackageReference Include="ReactiveUI.Events.WPF" Version="15.1.1" />
-    <PackageReference Include="ReactiveUI.Fody" Version="19.4.1" />
+    <PackageReference Include="ReactiveUI.Fody" Version="19.5.41" />
     <PackageReference Include="ReactiveUI.Validation" Version="3.1.7" />
     <PackageReference Include="ReactiveUI.WPF" Version="19.4.1" />
     <PackageReference Include="Splat.NLog" Version="15.2.22" />