[codex] add current time reminder delivery mode config (#30031)

```python
delivery_mode = "any_inference" # default
delivery_mode = "after_user_or_tool_output" # new mode
``` 

## Validation
- just test -p codex-core load_config_resolves_current_time_reminder
- just test -p codex-core
lock_contains_prompts_and_materializes_features

codex-rs/core/src/session/config_lock.rs

@@ -361,6 +361,7 @@ mod tests {
                 enabled: Some(true),
                 reminder_interval_seconds: Some(1),
                 clock_source: Some(codex_features::CurrentTimeSource::System),
+                delivery_mode: Some(codex_features::CurrentTimeReminderDeliveryMode::AnyInference),
                 sleep_tool: Some(false),
             }))
         );