fix: add newline to graph output (#6397)
### Description
Add a leading newline to the graph preamble. This is the same behavior
as
[Go](https://github.com/vercel/turbo/blob/main/cli/internal/graphvisualizer/graphvisualizer.go#L67)
### Testing Instructions
`single-package/graph.t` now passes (and other tests which use `--graph`
are closer to passing)
Got rid of the Rust codepath test as we now have a matching Rust/Go
codepath output
Closes TURBO-1607
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Co-authored-by: Chris Olszewski <Chris Olszewski>
