chore: cleanup WORKSPACE

This is a task related to eventual cleanup of WORKSPACE support. This will happen when the minimum supported version is bazel 9, that is the first version that removes the WORKSPACE support.

Q: when should that happen? I personally think that having that done when bazel 9 is released and a stable bazel version no longer has `WORKSPACE` is a good time.

The following is a list of random things that we would need to do:
- [ ] Remove entry_points in `whl_library`.
- [ ] `IS_BZLMOD_ENABLED` has to go.
- [ ] `TOOL_VERSIONS` has to probably go and we can migrate the config to `MODULE.bazel` instead.

这是一个与 Bazel 9 及移除 WORKSPACE 支持相关的未来清理工作。请检查列出的区域：whl_library 中的 entry_points、IS_BZLMOD_ENABLED、TOOL_VERSIONS，以及提议的 MODULE.bazel 配置。当 Bazel 9 成为最低支持版本后解决每个检查清单项目，即表示完成。

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