fix: nix flake lock outdated

[TroyKomodo]

The flake lock is using an older version of https://github.com/oxalica/rust-overlay

which at the time only supported rust version 2025-05-28
https://github.com/oxalica/rust-overlay/blob/d68a69dc71bc19beb3479800392112c2f6218159/manifests/nightly/default.nix#L508

This updates the lock and then adds a documentation to future bumpers to also update the lock when they change the version again.

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