fix: NO-ISSUE Add indentation rules for let and attrset

[akirak]

This PR adds some seemingly missing indentation rules.

Example indentation from

  inputs = {
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";| ⇐ cursor here
  };

to

  inputs = {
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    | ⇐ cursor here
  };

instead of indenting to

  inputs = {
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
| ⇐ cursor here
  };

Another example indentation from

  }: let
    supportedSystems = import systems;
    forAllSystems = nixpkgs-unstable.lib.genAttrs supportedSystems;| ⇐ cursor here
  in {

to

  }: let
    supportedSystems = import systems;
    forAllSystems = nixpkgs-unstable.lib.genAttrs supportedSystems;
    | ⇐ cursor here
  in {

instead of indenting to

  }: let
    supportedSystems = import systems;
    forAllSystems = nixpkgs-unstable.lib.genAttrs supportedSystems;
| ⇐ cursor here
  in {

[purcell]

Great, thanks!

[purcell]

Will go ahead and merge since this is trivial and a clean addition.