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.

从 issue 描述和链接的 bazel-examples pull request 开始，了解 OCI layout 以及 layers 如何在磁盘上暴露。查看 Python 测试设置及其对 Docker library 的使用，然后确定 testcontainers 如何将 OCI descriptors 和 blobs 直接加载到 daemon 中。完成的标准是：无需先构建 Docker-loadable tarball，即可测试本地 OCI images。