Add automated NuGet publishing workflow

[roku674]

[Copy Paste figured you'd want it here too] This PR adds a GitHub Actions workflow to automate NuGet package publishing.

What it does

• Triggers on push to master branch (or manual workflow dispatch)
• Compares the version in LiteNetLib/LiteNetLib.csproj against the latest version on NuGet.org
• If the version has changed, it builds, packs, and publishes to NuGet.org
• Skips publishing if version is unchanged (avoids "package already exists" errors)

Setup required

You'll need to add a NUGET_API_KEY secret to your repository settings:

1. Go to Repository Settings → Secrets and variables → Actions
2. Add a new secret named NUGET_API_KEY with your NuGet.org API key

How to publish a new version

1. Update the <Version> tag in LiteNetLib/LiteNetLib.csproj
2. Commit and push to master
3. The workflow will automatically detect the version change and publish

This workflow pattern is adapted from an open-source C# project that uses the same approach for automated NuGet publishing.

[roku674]

@RevenantX

[RevenantX]

It should not be automatic. As manual action i will include this

[RevenantX]

Also seems it need to use instead of