Include originator in plugin measurement analytics (#42445)

## What changed

- Add `originator` to plugin measurement inputs and emitted analytics events.
- Populate it from the turn originator when recording plugin measurements.
- Extend analytics tests to verify the originator is preserved in event payloads.

GitOrigin-RevId: 9998f829760222fc690dc8a10324794b5da27220

codex-rs/analytics/src/client_tests.rs

@@ -424,6 +424,7 @@ async fn api_key_auth_sends_only_plugin_events_to_codex_backend() {
                 thread_id: thread_id.to_string(),
                 turn_id: "turn-1".to_string(),
                 item_id: "item-1".to_string(),
+                originator: "codex_cli_rs".to_string(),
                 plugin_id: plugin_id.to_string(),
                 execution_id: "execution-1".to_string(),
                 operation: "security_scan".to_string(),
@@ -706,6 +707,7 @@ fn track_plugin_measurements_rejects_unbounded_inputs_before_queueing() {
         thread_id: "thread-1".to_string(),
         turn_id: "turn-1".to_string(),
         item_id: "item-1".to_string(),
+        originator: "codex_cli_rs".to_string(),
         plugin_id: "sample@openai-curated".to_string(),
         execution_id: "execution-1".to_string(),
         operation: "security_scan".to_string(),