Migrate to Bzlmod

As noted in the [Bazel documentation](https://bazel.build/external/migration):
> Bzlmod will replace the legacy WORKSPACE system. The WORKSPACE file is already disabled in Bazel 8 (late 2024) and will be removed in Bazel 9 (late 2025).

It would be nice to migrate the examples and other code to use Bzlmod. This should be trivial to do at least for the examples. For example, for the `local_arg_printer` example, just replacing `WORKSPACE` with the following `MODULE.bazel` should work:
```bzl
module(
name = "xmanager_local_arg_printer_example",
version = "1.0",
)

bazel_dep(name = "rules_cc", version = "0.1.2")
```

I would expect there to not be many changes needed from the core code either, but I think e.g. #46 might be related.