Changes

This PR adds a new rust-toolchain-nightly versioning scheme and a rust-nightly-version data source, based on the data from https://rust-lang.github.io/rustup-components-history/.

This PR was extracted from #38554, as requested in #38554 (comment).

Context

Please select one of the below:

• This closes an existing Issue, Closes: #
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

I did not find an open issue for this at first glance, but there are a couple of related issues/PRs/discussions:

• rust-toolchain version updates #11488
• Support rust-toolchain version updates specifically #24762
• feat(manager/rust-toolchain): Add support for rust toolchain versioning #32432

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

Please select one option and, if yes, briefly describe how AI was used (e.g., code, tests, docs) and which tool(s) you used.

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI generated non‑trivial portions of code, tests, or documentation).
• Yes — other (please describe):

I did use Claude Code for the initial draft, but reviewed, adjusted and tested everything manually afterwards.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository: https://github.com/Turbo87/renovate-rust-test/pulls?q=is%3Apr