Create universe MODULE.bazel input causes churn

Referring to `MODULE.bazel` in a `module_ctx` when an extension is non-reproducible means the `MODULE.bazel` hash appears in the `MODULE.bazel.lock`. This is major churn, with any unrelated `MODULE.bazel` change triggering the rules rust extension and diff in the `MODULE.bazel.lock` file.

This needs to be updated to use some other mechanism to find the root.
https://github.com/bazelbuild/rules_rust/blob/61f41867d5cada90aa7c415c8c3e550d51e8debe/crate_universe/extensions.bzl#L649