Upgrade targets to .NET 8/.NET 10, refresh MQTTnet packages, and add GitHub Actions CI/publish workflows

[Copilot]

This updates the library to target .NET 8 and .NET 10, moves the examples/tests to .NET 10, upgrades MQTTnet dependencies to the latest 5.1.* line, and replaces the existing external build badge with repository-native GitHub Actions. It also adds first-party CI and release workflows for branch/PR validation and package publishing to both NuGet.org and GitHub Packages.

• Framework and package baseline

  • Change the library target frameworks from net9.0;net8.0 to net8.0;net10.0
  • Move ExampleClient, ExampleServer, and test project targets to net10.0
  • Upgrade MQTTnet dependencies to floating 5.1.* patch versions
  • Include the repository README in the NuGet package metadata to remove package authoring warnings

• Warning cleanup

  • Enable nullable context consistently where nullable annotations were already used
  • Tighten null handling around route invocation and assembly discovery
  • Remove remaining compile-time/package warnings exposed by the framework/package updates

• GitHub Actions

  • Add ci.yml to build on all branch pushes and pull requests
  • Add publish.yml to pack and publish on release or manual dispatch
  • Publish packages to:
    • NuGet.org via organization secret NUGET_API_KEY
    • GitHub Packages via GITHUB_TOKEN
  • Scope workflow permissions explicitly

• Docs and repository metadata

  • Replace the old AppVeyor badge with a GitHub Actions CI badge
  • Update supported framework documentation to reflect .NET 8 and .NET 10

Example of the updated package targeting/version policy:

<PropertyGroup>
  <TargetFrameworks>net8.0;net10.0</TargetFrameworks>
  <PackageReadmeFile>README.md</PackageReadmeFile>
</PropertyGroup>

<ItemGroup>
  <PackageReference Include="MQTTnet" Version="5.1.*" />
  <PackageReference Include="MQTTnet.AspNetCore" Version="5.1.*" />
</ItemGroup>

[Copilot]

Pull request overview

Updates the library and its companion projects to newer .NET target frameworks, refreshes MQTTnet dependencies, and introduces first-party GitHub Actions workflows for CI and package publishing.

Changes:

• Retarget projects to net8.0/net10.0 (library multi-targeted; examples/tests moved to net10.0).
• Update MQTTnet package references to the 5.1.* line and include README.md in NuGet package metadata.
• Add GitHub Actions CI and Publish workflows and replace the AppVeyor badge with a GitHub Actions badge.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
Tests/MQTTnet.AspNetCore.Routing.Tests/MQTTnet.AspNetCore.Routing.Tests.csproj	Retarget tests to net10.0.
Source/Routing/MqttRouter.cs	Tighten null handling and improve error messages during handler invocation/parameter assignment.
Source/MQTTnet.AspNetCore.Routing.csproj	Switch TFMs to net8.0;net10.0, float MQTTnet deps to 5.1.*, and pack README.
Source/Extensions/ServiceCollectionExtensions.cs	Enable nullable context and harden assembly discovery fallback.
README.md	Swap build badge to GitHub Actions and update supported framework list.
ExampleServer/ExampleServer.csproj	Retarget example server to net10.0.
ExampleClient/ExampleClient.csproj	Retarget example client to net10.0 and float MQTTnet dependency.
.github/workflows/publish.yml	Add release/manual publish workflow (build/test/pack/push).
.github/workflows/ci.yml	Add CI workflow for restore/build/test on pushes and PRs.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.