Refactors the flake update script to consolidate root and dev lockfile
updates into a single commit. Changes include:
- Captures and normalizes `nix flake update` output.
- Removes reliance on `--commit-lock-file` and `--amend`.
- Eliminates the need to track or compare HEAD commits manually.
- Only commit when flake.lock, flake/dev/flake.lock, or
version-info.toml have changes.
This changes how we think about this directory; it does not need to be
exclusively for scripts related to updates, but should be a place for
any scripts intended to be run by CI workflows.
This mindset should make it easier to develop and test the business
logic of workflows, without always needing to test "in production" on
the nixvim repo or a fork.
