Track inference tool changes in turn analytics (#50964)

## What changed

Add `tools_change_count` to turn profiles and turn analytics events. Compare the full model-visible tool list before each sampling request, retaining the previous list across turns and connection resets. The first list establishes a baseline; subsequent changes increment the current turn's count.

## Testing

Add coverage for schema changes, tool additions, ordering changes, empty lists, and tracking across sessions and transport fallback. Extend the turn event serialization test to include `tools_change_count`.

GitOrigin-RevId: 44a15c42dc7d0b35c166666faeb9627b718b33dd

codex-rs/analytics/src/reducer.rs

@@ -3667,6 +3667,7 @@ fn codex_turn_event_params(
         after_last_sampling_ms,
         sampling_request_count,
         sampling_retry_count,
+        tools_change_count,
     } = profile;
     let token_usage = turn_state.token_usage.clone();
     let codex_error = turn_state.codex_error.as_ref();
@@ -3750,6 +3751,7 @@ fn codex_turn_event_params(
         after_last_sampling_ms,
         sampling_request_count,
         sampling_retry_count,
+        tools_change_count,
         duration_ms: completed.duration_ms,
         started_at,
         completed_at: Some(completed.completed_at),