tex-fmt: add module

[WGUNDERWOOD]

tex-fmt is a LaTeX source code formatter written in Rust, and uses a user configuration file in the .toml format.

Description

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[WGUNDERWOOD]

This is a draft PR which is waiting for NixOS/nixpkgs#363212 to be merged.

Edit: the PR at NixOS/nixpkgs#363212 has been merged, so this PR is ready for review.