Cannot resolve NuGet package references to local packages

Many monorepo enthusiasts insist that dependencies are checked into the source control system. The .NET ecosystem supports this by use of a custom NuGet feed. In Visual Studio, this can be achieved by creating a file called `NuGet.config` XML file and adding a `` element that contains a reference to the directory on disk containing the `.nupkg` files. In the IDE, this shows up as an entry in the Package Sources list of the NuGet Package Manager window.

Additionally, this would allow users to use internal packages not published to nuget.org, as there is currently no way to do this. The use case here is a version of a package where the maintainer either has not or will not accept bug fixes, and the development team maintains a forked version of the dependency project. There may not be any need for the development team to build this dependency as part of the target project, and the dependency code should not be a part of the target project.

Start by tracing the existing NuGet package-resolution entry points in rules_dotnet; the issue names NuGet.config and its packageSources element as the expected configuration. Confirm how a local directory feed and an internal forked package should be selected, then verify that packages resolve without adding their source code to the target project. No repository file or test is named in the issue.

Written by the indexing model from the issue text.