[cost.rates.providers.models.<type>.<model>] — token-cost rates
per (provider type, model). One slot per provider type; each
slot is a HashMap<model_id, ModelCostRates>. The slot list
matches ModelProviders byte-for-byte (same source macro).
Typed TTS-provider container — one slot per TTS family. Mirrors
ModelProviders but smaller (TTS has a closed set of 5 families:
openai, elevenlabs, google, edge, piper). No catch-all needed.