Unreleased sections get removed without changes to release spec

If you save and quit the release spec without making changes to it, the tool will proceed, only it will remove the Unreleased section of each package's changelog.

The tool should remove the release spec from the temporary directory if it detects that all packages have been set to `null` or `intentionally-skip` or if `packages` is an empty array, then produce an error.

Start by tracing the CLI flow that saves the release spec and removes or preserves package changelog Unreleased sections. Check how the temporary directory and package values are handled when all packages are null, intentionally-skip, or the packages array is empty. Done means the temporary release spec is removed and an error is produced without removing Unreleased sections when no changes were made.

Written by the indexing model from the issue text.