In my free-time for the past several years, I've been working on building a NuGet client from scratch that runs entirely within the Unity Editor.
I have finally launched NuGet For Unity onto the Unity Asset Store. It is completely free and open-source, so have at it!
Asset Store: https://assetstore.unity.com/packages/tools/utilities/nuget-for-unity-104640
Source Code: https://github.com/GlitchEnzo/NuGetForUnity