oci_load drops empty strings in cmd list

The `oci_load` rule seems to drop empty strings from the `cmd` list. This doesn't happen with rules_docker `container_image` rule.

The empty string behavior is useful for Java libraries like JCommander that help parse command line args.

### To reproduce

WORKSPACE
```
oci_pull(
name = "distroless_java21",
digest = "sha256:ed5be62a70c5b99708b4ad0fc53bda628d11e46e917f66720fd218cae8fe1568",
image = "gcr.io/distroless/java21-debian12",
)
```

BUILD
```
load("@rules_oci//oci:defs.bzl", "oci_image", "oci_load")

oci_image(
name = "test_image",
base = "@distroless_java21",
cmd = [
"hello",
"",
"goodbye",
"",
],
)

oci_load(
name = "test_image_load",
image = ":test_image",
repo_tags = [
"test_image:latest",
],
)
```

```sh
$ bazel run :test_image_load
$ docker inspect test_image:latest
...
"Config": {
"Cmd": [
"hello",
"goodbye"
],
"Entrypoint": [
"/usr/bin/java",
"-jar"
],
...
```

**Notice the empty strings are missing in the CMD list.**

* rules_oci v2.2.6
* Bazel version 6.5.0
* Docker version 28.4.0, build d8eb465

Start by running the supplied WORKSPACE and BUILD reproduction with Bazel, then inspect the resulting image using docker inspect. Compare oci_load's Cmd output with the declared cmd list and the rules_docker container_image behavior; done means empty strings are preserved in the loaded image's Cmd list.

Written by the indexing model from the issue text.