FR: incremental loader

I witness the following error while trying to run a container test against a tarball created by `rules_oci`.

```
➜ mre-container-tar-test git:(main) ✗ bazel test //my_package:empty_file_image_tarball_test
ERROR: /Users/josalvatorre/code/mre-container-tar-test/my_package/BUILD.bazel:26:25: in container_structure_test rule //my_package:empty_file_image_tarball_test:
Traceback (most recent call last):
File "/private/var/tmp/_bazel_josalvatorre/bb1e2552732b81b1b69870fcd931a2e6/external/container_structure_test~/bazel/container_structure_test.bzl", line 55, column 17, in _structure_test_impl
fail("when the 'driver' attribute is not 'docker', then the image must be a .tar file")
Error in fail: when the 'driver' attribute is not 'docker', then the image must be a .tar file
ERROR: /Users/josalvatorre/code/mre-container-tar-test/my_package/BUILD.bazel:26:25: Analysis of target '//my_package:empty_file_image_tarball_test' failed
ERROR: Analysis of target '//my_package:empty_file_image_tarball_test' failed; build aborted
INFO: Elapsed time: 0.079s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
ERROR: Build did NOT complete successfully
ERROR: No test targets were found, yet testing was requested
```

This *only* happens when testing against a tarball. I can test against the image layer just fine.

I created a simple [minimal reproducible example here][1].

This might just be an issue with [`container_structure_test`][3]. In that case, we can just mention in the documentation that we only support testing against the image layer instead of the tarball.

Sorry if I'm just doing something wrong 😅

[1]: https://github.com/josalvatorre/mre-container-tar-test
[2]: https://github.com/bazel-contrib/rules_oci/blob/3d43cb1a1bb2f5edc15c7f48b406be3fb225e673/README.md?plain=1#L95-L97
[3]: https://github.com/GoogleContainerTools/container-structure-test#running-structure-tests-through-bazel

Start with the linked minimal reproducible example and its my_package/BUILD.bazel target, then read the referenced README lines and container_structure_test Bazel documentation. Compare testing the image layer with the tarball case and determine whether rules_oci or container_structure_test owns the limitation. Done means the behavior is fixed or the supported input is clearly documented.

Written by the indexing model from the issue text.