Refactor network_inspectors.py for modularity and testability

[cpaniaguam]

Introduce an initial modular package layout for network inspection functionality so future changes don’t accumulate in one large file.

Currently the file mixes network loading, data generation (grids/manifolds), simulator orchestration, and low-level plotting logic. Not surprisingly, the two orchestrator functions kde_vs_lan_likelihoods and lan_manifold have large signatures.

Some initial ideas for the refactor: Data/Config Pattern

1. Config Objects: Encapsulate model metadata (predictor, name) and plotting defaults (font scale, size) to reduce signature bloat.
2. Pure Computation: Isolate RT grid generation and likelihood calculations into "headless" functions.
3. Thin Wrappers: Refactor existing entry points to use these new computation helpers for rendering.

[linear-code]

HSSM-652