Inspect what contributes to `bzlTransitiveDigest` in module lock file

### Description of the feature request:

Have a way to see all the inputs that go into `bzlTransitiveDigest`.

### Which category does this issue belong to?

External Dependency

### What underlying problem are you trying to solve with this feature?

Debug why that value changes when it unexpectedly does so.

### Which operating system are you running Bazel on?

Linux

### What is the output of `bazel info release`?

release 7.4.1

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.

_No response_

### What's the output of `git remote get-url origin; git rev-parse HEAD` ?

```text
git@github.com:sourcegraph/sourcegraph.git
31c7d91aa239eee3a89e508168ff60ac2a752e80
```

### Have you found anything relevant by searching the web?

https://bazelbuild.slack.com/archives/C014RARENH0/p1742374651081339

### Any other information, logs, or outputs that you want to share?

I was running into an issue were for one extension (rules_rust) I get a different value just on this field and nothing else. The difference was between two systems I was running.

They had the same version of bazel, but managed in slightly different ways so I was curious to see why the hash changed between the systems.

Start by tracing how Bazel computes bzlTransitiveDigest for the module lock file, using the rules_rust case and the linked Slack discussion as context. Determine which inputs need to be inspectable and define a user-visible way to report them; done means users can explain why the digest differs between systems.

Written by the indexing model from the issue text.