update GitHub action versions and NuGet packages, bump version

[ryanrivest]

This should resolve the build failure caused by outdated .NET Core 3.1.301 that prevented the recent library update from publishing.

• Updated GitHub Actions to use current versions (checkout@v5, setup-dotnet@v5, alirezanet/publish-nuget@v3.1.0) and changed dotnet-version to 8.0.x
• The build workflow will also run now when a PR is created, but the package is only published when it's merged
• Changed test projects to .NET 8 and applied some package version updates
• Fixes: No usable version of libssl was found error
• Updated project version to 1.0.3