Add GO term level information to enrichment results

[Moonerss]

Currently, clusterProfiler's GO enrichment analysis results do not include the GO term level from the GO ontology hierarchy. Adding this information would greatly help users filter, interpret, and visualize results—for example, by focusing on terms at a specific depth (e.g., levels 3–6) or by coloring terms by level in graphs.

Thank you for your consideration and for maintaining this excellent package!