Update GTFS-RT protobuf: deprecate active_period, add communication/impact periods

Sync gtfs-realtime.proto with google/transit master and regenerate the
Elixir .pb.ex (protoc-gen-elixir 0.15.0, matching mix.lock). The Alert
message now deprecates active_period and adds communication_period and
impact_period.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: vdegove

apps/transport/lib/transport/protobuf/gtfs-realtime.pb.ex

@@ -400,7 +400,20 @@ defmodule TransitRealtime.Alert do
   field(:active_period, 1,
     repeated: true,
     type: TransitRealtime.TimeRange,
-    json_name: "activePeriod"
+    json_name: "activePeriod",
+    deprecated: true
+  )
+
+  field(:communication_period, 2,
+    repeated: true,
+    type: TransitRealtime.TimeRange,
+    json_name: "communicationPeriod"
+  )
+
+  field(:impact_period, 3,
+    repeated: true,
+    type: TransitRealtime.TimeRange,
+    json_name: "impactPeriod"
   )
 
   field(:informed_entity, 5,

apps/transport/lib/transport/protobuf/gtfs-realtime.proto

@@ -625,7 +625,18 @@ message Alert {
   // Time when the alert should be shown to the user. If missing, the
   // alert will be shown as long as it appears in the feed.
   // If multiple ranges are given, the alert will be shown during all of them.
-  repeated TimeRange active_period = 1;
+  // Should not be used - for backwards-compatibility only.
+  repeated TimeRange active_period = 1 [deprecated = true];
+
+  // Time when the alert should be shown to the user strictly for informative reasons.
+  // If missing, the consuming application can decide when it's appropriate to be shown.
+  // If multiple ranges are given, the alert will be shown during all of them.
+  repeated TimeRange communication_period = 2;
+
+  // Time when the services are affected by the alert. If communication_period is specified,
+  // every time interval in impact_period must be fully contained within at least
+  // one time interval of communication_period.
+  repeated TimeRange impact_period = 3;
 
   // Entities whose users we should notify of this alert.
   repeated EntitySelector informed_entity = 5;