Migrate bazel from WORKSPACE to bzlmod

the current bazel setup uses a mix of WORKSPACE and bzlmod configuration ... WORKSPACE is deprectated and will be dropped by bazel in a couple of months with current runs of bazel displaying this warning message.

```
WARNING: WORKSPACE support will be removed in Bazel 9 (late 2025), please migrate to Bzlmod, see https://bazel.build/external/migration.
```