chore(nix): use mkShellNoCC and update flake inputs

[ryoppippi]

Summary

• Switch from mkShell to mkShellNoCC for lighter devShell (no C compiler needed)
• Update all flake inputs to latest versions

Test plan

• Run nix develop and verify the shell works correctly

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Summary by cubic

Switch to a lighter Nix dev shell by replacing mkShell with mkShellNoCC, reducing dependencies and speeding up shell activation.

^{Written for commit c7c5671. Summary will update on new commits.}

[Copilot]

Pull request overview

This pull request simplifies the Nix development environment by removing the complex uv2nix-based Python environment management in favor of a lighter approach using mkShellNoCC and letting uv handle Python dependencies directly. It also updates all flake inputs to their latest versions.

Changes:

• Switched from mkShell to mkShellNoCC for the development shell, removing C compiler dependencies
• Removed uv2nix, pyproject-nix, and pyproject-build-systems flake inputs and their associated Python version-specific virtual environments
• Updated CI workflow to add explicit dependency installation steps and simplified caching strategy

Reviewed changes

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
flake.nix	Removed uv2nix integration, switched to mkShellNoCC, simplified devShell configuration to use uv directly
flake.lock	Updated all flake inputs to latest versions, removed uv2nix-related dependencies
justfile	Removed dynamic _run helper, hardcoded uv run commands, removed lint-fix alias
.github/workflows/ci.yaml	Updated Python version matrix format, added explicit dependency installation steps, removed Python version from dev shell invocations
.github/actions/setup-nix/action.yaml	Removed python-version input, switched from cache-nix-action to cachix-action for caching

Comments suppressed due to low confidence (1)

flake.nix:118

• The condition compares uv.lock (a file) with .venv (a directory) using the -nt (newer than) operator. The -nt operator is meant to compare modification times of files. When comparing a file to a directory, the behavior may be unexpected - it compares against the directory's metadata modification time, not the modification time of its contents.

Consider checking against a specific file within .venv that gets updated when dependencies are installed, such as .venv/pyvenv.cfg or .venv/.complete (a marker file you create after successful installation).

              if [ ! -d .venv ] || [ uv.lock -nt .venv ]; then

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