Persist response token usage in rollout history (#41912)

## Why

Resumed threads need to continue per-turn and per-thread token totals without scanning arbitrarily far beyond the latest compaction checkpoint.

## What changed

- Add durable `TokenUsageRecord` rollout items with response, turn, thread, session, and root-turn attribution.
- Restore accumulated usage on resume and snapshot the latest record plus the compaction response ID in compaction checkpoints.
- Preserve root-turn lineage in persisted turn context, while ensuring forked child threads start with their own usage totals.

## Testing

- Cover usage accumulation across multiple responses and resumed turns.
- Cover local and remote compaction checkpoints, invalid remote compaction output, rollout reconstruction, and fork isolation.

GitOrigin-RevId: ef9e0c4a9102a08a2c382be4cdac68c84353c90a

codex-rs/rollout/src/model_context.rs

@@ -160,7 +160,8 @@ impl ModelContextScan {
             | RolloutItem::SessionMeta(_)
             | RolloutItem::InterAgentCommunicationMetadata { .. }
             | RolloutItem::RealtimeItem(_)
-            | RolloutItem::SecurityRiskScore(_) => {}
+            | RolloutItem::SecurityRiskScore(_)
+            | RolloutItem::TokenUsageRecord(_) => {}
         }
 
         if self.has_bounded_cutoff() {