refactor: decompose _build_tcs_tree into structural and property-populating helpers

[bhagathkrishnacdac]

Description
This PR refactors _build_tcs_tree to address cognitive complexity and simplify scheduling hierarchy visualization. The original monolithic function, which managed tree node construction, relationship linking, policy checking, and string formatting in multiple redundant loops, has been divided into focused, single-responsibility helpers.

Key Changes

• Separated Node Construction: Extracted _create_tc_node to construct standard dictionary nodes for individual traffic classes.
• Isolated Topology Mapping: Extracted _build_parent_child_relationships to handle the recursive linking of parent and child traffic classes in the tree.
• Decoupled Property Formatting: Extracted _populate_show_list to handle policy-specific formatting (e.g., parsing weighted_fair shares, priority values, and rate limits/burst metrics).
• Streamlined Orchestrator: Simplified _build_tcs_tree into a linear, three-step execution pipeline.