use toolchain files as single source of truth

[sectore]

for Rust versions (default + nightly).

Problem

Currently Rust versions (default + nightly) are defined all over the place. Check PR #1638 and you will know.

Fix

Use two toolchain files for default and nightly as a single source of truth

Changes

• Add another rust-toolchain-nightly.toml (besides default rust-toolchain.toml)
• Extend justfile to get Rust versions from toolchain files.
• In .github/workflows/*.yml files use actions-rust-lang/setup-rust-toolchain to handle different toolchain files (instead of hard-coded Rust versions)
• Ignore .direnv folder created by direnv / Nix users
• flake.nix: Add missing dependencies, fix deprecated xorg packages
• Run nix flake update to get latest inputs, especially latest Rust versions.

TODO

• Check if CI/GH workflows still work DONE

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.30%. Comparing base (e735044) to head (dc727ad).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1791   +/-   ##
=======================================
  Coverage   61.30%   61.30%           
=======================================
  Files         310      310           
  Lines       39433    39433           
=======================================
  Hits        24174    24174           
  Misses      15259    15259           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[marc2332]

Why did you make this specific change? Like, how did you end up finding this "issue", solving it and opening a PR? Because, if I have to be honest, this looks AI generated. I am in favor of AI, but against slop.

[sectore]

As a Nix user I have to figure out how to run this project, especially by having different toolchain. This PR includes all changes I needed. It's not AI generated (no vibe-coding), but I have paired w/ Claude.

If you think it's slop to be more DRY, just ignore/close it. Changes are based on few hours work btw, AI would not do that in this way. Instead AI is still happy to put same versions/hashes everywhere and at different places (which is more than questionable). Call it human experiences vs. AI. Hope this PR makes more sense now.