Introduce a better hash function for Starlark

### Description of the feature request:

See https://github.com/bazelbuild/bazel/pull/26528#discussion_r2200777193

### Which category does this issue belong to?

_No response_

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

_No response_

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

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

_No response_

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

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

```text

```

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

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

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Start with the discussion linked from the issue in pull request 26528, especially the referenced comment, to determine the intended Starlark hash behavior. The issue names no files, tests, or entry points; done means agreeing on the hash-function design and implementing it with coverage for the expected behavior.

Written by the indexing model from the issue text.