Feature: read OCI images from the disk without requiring a tarball

What are you trying to do?

Under Bazel, or other local-only build systems, an image is constructed as a series of layers which are only on the disk, not pushed to any remote docker registry.

To test such an image, one option is to create a tarball format that's suitable for docker load. Then in the Setup of the python test, you can use the docker library from Pypi to do that docker load.
However, constructing the tarball is an expensive operation. In particular as Bazel has distinct build steps that can run remotely and have cached results, we get a massive file for a typical user image that has to be stored on a network location. Building the tarball should not be required, it's just a way to be docker load-compatible.

Instead, we could teach testcontainers how to read the OCI format, which is a JSON descriptor pointing to the layers as blobs. These could be loaded into the daemon directly.

https://github.com/aspect-build/bazel-examples/pull/306 shows how this looks.

issue の説明とリンクされた bazel-examples pull request から始めて、OCI layout と、layers がディスク上でどのように公開されるかを理解します。Python のテスト設定と Docker library の使用方法を確認し、そのうえで testcontainers が OCI descriptors と blobs を daemon に直接読み込めるようにする方法を判断します。ローカルの OCI images を、まず Docker-loadable tarball を構築することなくテストできれば完了です。