Deterministic ci

[seddonym]

Prior to this, the CI runs weren't deterministic:

• The Python libraries weren't guaranteed to be the same (they would update automatically) due to no uv.lock file.
• The Ruff toolchain wasn't guaranteed to be the same.

This adds a uv.lock file which was added to .gitignore in error, and a rust-toolchain.toml to pin the rust version. It also fixes some minor issues picked by by clippy under the latest toolchain.

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 23 skipped benchmarks¹

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_{Comparing deterministic-ci (6a45cdd) with main (00bd8b5)}

Footnotes

1. 23 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩