chore(deps): Update flake.lock

[RasmusRendal]

This apparently includes some changes to nixfmt.

[cursor]

PR Summary

Medium Risk
Lockfile bumps for nixpkgs and rust-overlay can change toolchains and package builds across consuming repos, even though the Nix source edits are formatting-only.

Overview
Updates flake inputs in flake.lock, including nixpkgs (26.05 channel), rust-overlay, treefmt, flake-parts, github-actions-nix, nixpkgs-lib, and wrappers.

Reformats many Nix modules to the denser brace style produced by the newer nixfmt --strict (e.g. { lib, ... }: { instead of a split header). No behavioral logic changes in those files.

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