- Add seed() method to ModelUsageTracker for bulk-loading persisted entries at startup
- Create PostgresModelUsageStore for persistence of model usage counters to Postgres
- Store only current cumulative snapshots (no historical time-series)
- Use standard CREATE TABLE IF NOT EXISTS idiom matching other Postgres stores
- Add comprehensive mocked unit tests for both components
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Implement manual generator driving using next()/StopIteration to capture
the return value (trailing usage dict) from inner stream_chat() implementations,
enabling token tracking for streaming LLM calls.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
