Add Dockerfile and CI for Docker image: Build development environment image based on gocnn/gocu

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Add Dockerfile and CI for Docker Image

Create a Dockerfile and corresponding CI workflow to automate the build of a Docker image for the candy development environment. This image should be based on the gocnn/gocu Docker image and contain all dependencies required for candy development, including:

• Go
• candy source code and dependencies
• CUDA, cuDNN, Metal (if cross-platform support is planned)
• Any additional tools needed for building or testing

Tasks

• Author a Dockerfile in the repository root
• Write a CI workflow (e.g., GitHub Actions) to build and, optionally, publish the image
• Ensure the Docker image is efficiently layered and can be easily maintained
• Document how to use and customize the Docker image in the README

Reference: Use the gocnn/gocu Docker setup as the image base and adapt for candy development needs.