Create NuGet packages for core MLIR.NET and MLIR.Generators

[jonathanvdc]

Summary

Create NuGet packages for:

1. The core MLIR.NET library, making it distributable as a reusable package.
2. The MLIR.Generators source code generator, so it can be included and consumed via NuGet.

Why

• Facilitates wider, simpler adoption and integration of MLIR.NET and its code generator.
• Eases dependency management for projects consuming MLIR.NET and MLIR.Generators.

Tasks

• Add or modify project files and build scripts to support packaging for both projects.
• Ensure correct dependencies, versioning, and metadata for both packages.
• Publish to a NuGet feed (test feed and/or nuget.org, as suitable).
• Document the packaging and publishing process in the repository.
• Configure GitHub Actions to automatically build and publish NuGet packages whenever a tag is pushed to main.

Acceptance Criteria

• Both packages can be built and published locally and to nuget.org.
• Documentation for users on how to consume the packages.
• Versioning and dependencies are handled correctly for both packages.
• GitHub Actions is configured to automatically build and publish NuGet packages.