refactor: decompose _draw_pipeline and isolate metric-formatting calculations

[bhagathkrishnacdac]

Description
This PR refactors _draw_pipeline to address cognitive complexity and improve code readability. The logic that formats Graphviz descriptions and evaluates rate differentials for real-time monitoring has been separated from the subprocess execution and IPC stream pipeline.

Key Changes

• Isolated Label Generation: Extracted _get_node_labels to manage the assembly of multi-line module descriptors (names, classes, descriptions).
• Decoupled Metric Evaluations: Extracted _get_gate_label to calculate either static counts or active rate differentials (Megabits/packet metrics) and return standard string formats.
• Simplified Process Piping: Streamlined the main _draw_pipeline function to focus strictly on spawning graph-easy via subprocess.Popen and streaming the pre-calculated node and edge configurations to standard input.