Pretty error reporting

[angelcerveraroldan]

The goal of this PR is to add pretty error reporting, since the difference is visual, I have attached screenshots for the errors that butane would report for the following butane:

variant: fcos
version: 1.6.0
boot_device:
  layout: s390x-virt
  mirror:
    devices:
      - /dev/vda
      - /dev/vdb
systemd:
  units:
    - name: example.service
      enabled: true
      contents: |
        [Unit]
        Description=Example
      contents_local: example.service
    - name: other.service
      dropinz:
        - name: override.conf
          contents: |
            [Service]
            ExecStart=
    - name: valid.service
      enabled: true

How errors show without this feature:

How errors show with the new feature:

New flags added:

1. --pretty-errors to turn on pretty error reporting
2. --color[=WHEN], where WHEN is auto (default), always, or never. This follows the same convention as ls, ripgrep, diff, bat, exa, ... In auto mode, colors are disabled if stderr is not a terminal or if the NO_COLOR environment variable is set. It also accepts colour just in case

This is an early PR to get feedback on whether or not this is a good addition to butane, or if it should go somewhere else / nowhere. I am not sure if the current flag name pretty-errors is good or not, seems kind of verbose to me.

[gemini-code-assist]

Code Review

This pull request introduces a new reporting package to provide enhanced, "pretty" error messages with source code context and ANSI colorization. The main entry point is updated to track input filenames and utilize these formatting options. Key feedback points include resolving a package name conflict that prevents compilation, implementing bounds checking for string slicing to avoid runtime panics, dynamically managing colorization for non-TTY outputs, and ensuring error underlines remain visible when pointing to whitespace.