[o11y] Add undefined to tailStream return types

Returning undefined indicates that tail events for the given worker event can be
ignored, which is used to shut down the tail stream early as an optimization.

Author: fhanau

types/defines/rpc.d.ts

@@ -243,7 +243,7 @@ declare namespace CloudflareWorkersModule {
     queue?(batch: MessageBatch): void | Promise<void>;
     scheduled?(controller: ScheduledController): void | Promise<void>;
     tail?(events: TraceItem[]): void | Promise<void>;
-    tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+    tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }

types/generated-snapshot/experimental/index.d.ts

@@ -16196,7 +16196,8 @@ declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }

types/generated-snapshot/experimental/index.ts

@@ -16137,7 +16137,8 @@ export declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }

types/generated-snapshot/index.d.ts

@@ -15913,7 +15913,8 @@ declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }

types/generated-snapshot/index.ts

@@ -15854,7 +15854,8 @@ export declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }