Scaffold multi-target Tekmetric NuGet library and CI packaging workflow

[Copilot]

This PR introduces a C# class library suitable for NuGet distribution and configures it to target both modern .NET (net10.0) and legacy .NET Framework (net45). It also adds a GitHub Actions pipeline to build and pack the library consistently.

• Library scaffolding

  • Added a new SDK-style class library project under Tekmetric/.
  • Kept the surface minimal (Class1.cs) to establish the package baseline without adding extra API shape.

• Targeting + package metadata

  • Updated project configuration to multi-target net10.0;net45.
  • Added package metadata (PackageId, Authors, Description, PackageReadmeFile).
  • Included repository README.md in the packed .nupkg.
  • Added Microsoft.NETFramework.ReferenceAssemblies for net45 builds in non-Windows environments.

• GitHub Actions pipeline

  • Added .github/workflows/ci.yml to run restore/build/pack and publish package artifacts.
  • Set explicit workflow token permissions (contents: read) for least-privilege defaults.

• Repository hygiene

  • Added .gitignore entries for bin/, obj/, and artifacts/ to avoid committing build outputs.

<PropertyGroup>
  <TargetFrameworks>net10.0;net45</TargetFrameworks>
  <PackageId>Tekmetric</PackageId>
  <PackageReadmeFile>README.md</PackageReadmeFile>
</PropertyGroup>

<ItemGroup Condition="'$(TargetFramework)' == 'net45'">
  <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="All" />
</ItemGroup>

Original prompt

I want to create a .NET Standard class library authored in C#. It should support .NET 10.0 and .NET Framework 4.5. It will be a nuget package and needs a github actions pipeline.