fix(validate): return correct node_id for nodes without a label

[bhuvan-somisetty]

Fixes #592

The node id was sliced out of the warning with a fixed -9, but has no label is 13 chars, so JSON output gave "n1 has" instead of "n1". Now slices by the actual suffix length.

Added a test that checks node_id and nodes_affected for an unlabeled node.

[bhuvan-somisetty]

@pradeeban thanks for reviewing and merging the last few PRs, really appreciate it.

I've mostly been picking up smaller bugs in the CLI and the Python runtime so far. Is there any area you'd like me to focus on more going forward? Could be a part of the codebase that needs more attention, or something bigger on the roadmap you'd want help with. Happy to go wherever it's most useful.